When the long, perpendicular side of a right triangle is wrapped along the circumference of a cylinder through its base, the hypotenuse of the triangle forms a helix (curve) on the cylinder. The profile that will be formed when channels are opened in equal distances on the cylinder along this helix line in the forms of triangles, squares, trapezoids etc is called a screw. The base of the triangle corresponds to the periphery of cylinder BS and its height AC corresponds to pitch screw as seen in Figure one.
Screws are machine elements that have become a part of our daily life in all aspects especially as parts that form the threaded sections of connection elements. Screws are produced in different profiles depending on the importance of their function. Screws are divided into 5 main groups according to their profiles, hence thread forms;
a) Triangular Screws
b) Trapezoid Screws
c) Square Screws
d) Saw Screws
e) Circular Screws.

In addition to these, there are also wooden and cast screws in different profiles. However, these bolts are not handmade; they are produced automatically in special machines.

a) Triangle Screws

Triangle screws are screws with their external profile in the form of a triangle as its name calls. The triangular angles constituting the threads of triangular screws are large and helix angles are small. Helix pitches of screws and thread heights of screws are small based on the size of helix angles. Production of triangle screws with these features is due to their necessity to be in tightened position at all times. Hence, the necessity of remaining tight of a connection made by using a screw (names as auto blockage) has led to the constitution of triangle screws with small pitch. There are two different types of triangle screws, namely metric and whitworth. The most important feature distinguishing these two types from each other is the angle of screws. Triangular angle of metric screws is 60° and triangular angle of whitworth screws is 55°. Hence, a thread of a metric screw is an equilateral triangle and a thread of a withworth screw is an isosceles triangle.

Pitch of a screw is the most significant component of the screw. A screw is expressed in terms of its pitch. A pitch comprises of a full part and thread of a thread. Pitch is expresses in terms of millimeters in metric screws and in terms of division of one finger length to the number of threads in whitworth screws. All elements of both types of screws are calculated according to their number of pitch. The tip of the thread is cut flat and the base is rounded in metric screws. In whitworth screws however both the tip of the thread and the base is rounded. Rounding the base of the screws is implemented to facilitate manufacturing of the screw and increase its resistance. As it can also be understood from these definitions, the thread height of the screw is the distance between the upper part of the screw and the base.

Helix angle is the angle that constitutes the pitch of the screw. As mentioned above, helix angles of normal triangle screws are small. The fact that helix angles are small increases the auto blockage of the screw. For this reason, once triangular screws are screwed tightly, they are not easily unfastened with the effect of shocks. Both metric screws and whithworth screws are produced in two different forms with fine thread and normal thread to increase this feature of the screws. If screws are metric, they are called metric fine thread and if they are whitworth, then they are called whitworth fine thread. There are also screws with larger helix angle. But these are not connection screws, they are movement screws.

b) Trapezoid Screws

The thread form of trapezoid screws is the form of a cutoff triangle as seen in the figure. For this reason, the threads of screws and nuts clasp each other without gap. Trapezoid screws are generally used as movement screws due to this feature.

The fact that threads are in the form of cut off triangles in trapezoid screws provides the opportunity for transmission of movement without any gap and also the possibility to unscrew easily when needed. Therefore, trapezoid screws are preferred in parts that need to be screwed and unscrewed frequently. (For instance, clamp screws used for machining production ) The norm of tip angles of trapezoid screws is TS61/ 23 and DIN 103  as 30 with name metric-iso trapezoid screw. The measurements of normal trapezoid screws produced as per this norm are given in Table 1. Trapezoid screws are shown in the form of “Tr 24*5 “. In this expression Tr designates that the screw is trapezoid, 24 corresponds to the external diameter of the screw and the number 5 shows that the pitch of the screw is 5.

To summarize the explanations given above, the helix angles of trapezoid angles are large and their tip angles are small. Therefore, the frictional force between the threads would be small as well. For these reasons, trapezoid screws are used as movement screws. They are not used as connection screws.

c.) Square screws

Square screw means a screw with its cross section taken parallel to its axis the external profile of which is in the form of a square. Just like triangular screws, square screws are not connection screws they are used as movement screws since the lateral surfaces of square threads cannot provide sufficient compression force as they are perpendicular to the axis of the screw, furthermore, the surfaces of threads are shorter in square screws, therefore friction would be less between external surfaces.

As it can also be understood from the figure, the pitch of the screw comprises of a full part of the thread and a cavity of the thread and is expressed as p. The helix angle of square screws is significant for auto blockage of screws. The screw cannot remain in tightened position if the helix angle is large. It is unscrewed easily by itself or after a small shock. If the helix angle is small, the screw can remain tight. However, it can still be unscrewed with the effect of a shock or a shake.

Since square screws are used as movement screws, they are produced as single jaw or multiple jaw depending on their place of use.

Since the pitch of a screw comprises of a full part of a thread and a cavity of the thread, the height of the thread is as much as half the pitch. There is a small space of 0.1-0.3mm in square screws between the upper part of the thread and its base. This provides the screw with the opportunity to work comfortably. Square screws do not have norms. For this reason, there is no connection between diameters of upper part of threads and pitches. However, still the pitch of the screw should conform to the diameter of the upper part of the thread.

2. Screw Norms

Since screws are the machine equipments used most frequently in the industry, their norms are prepared in various types and measures. Therefore, norms are produced according to norm measures in every country. Establishment of norms for screws means that a screw has been produced by each manufacturer in the same measurement. A screw with norm is called a normal screw. Screws that do not have norms are called special norms. However, the elements of special screws are calculated according to formulas with norms.
Screws are generally produced according to DIN norms in the whole world. However, today countries established a world standard organization (ISO) that covers many technical aspects and have included metric screw within the scope of this norm. The industry of all countries benefits directly from both DIN and also ISO norms. However, Din and ISO norms have been translated to their own languages in each country and are being used as they are since language problems occur. The Turkish Standards Institution in our country prepared the TS 61 screw norms in conformity with the DIN norms.

Screw norms used in the world industry today are as follows.

1. metric normal screw TS61/DIN 13
2. metric fine thread screw TS61/8-4 DIN13
3. whitworth screw TS61/16 DIN11
4. whitworth pipe screw TS61/20 DIN259
5. trapezoid screws TS 61/23 DIN103
6. saw screws TS 61 /30 DIN513
7 . circular screws TS61/32 DIN 405

Symbols of screws and meanings of these symbols and their area of use are given in the table below.

designation name meaning of symbols areas of usage
M 16 Metric normal screw M. means that it s a metric screw, 16 designates that the diameter is 16 mm as connection screw
M 22x1,5 Metric fine screw M. means that it is a metric screw, 22 corresponds to the diameter of the screw ( mm ), 1,5 stands for the pitch of the screw Where diameter of base of thread with small pitch is required
1 x 1/4 whitworth screw 1 x 1/4 diameter of the screw in terms of inches Connection screw
R x 1/2 whitworth pipe screw R pipe screw, 1/2 diameter of screw in terms of inches Used in pipe connections
Tr 24 x 5 Trapezoid screw Tr designates that it is a trapezoid screw, 24 is the diameter of the screw in terms of mm, 5 stands for pitch of the screw movement screws required to be tightened in each direction
S 36 x 6 saw screw S designates that it is saw screw, 36 shows the diameter of the screw, 6 stands for the pitch of the screw It is used for connections that exert force on one side
Rd36 x 1/4 Circular screw Rd circular screw, 36 shows the diameter of the screw, 1/4 designates the pitch of the screw in terms of inch It is used in places that are easily polluted such as trains and similar vehicles

2.1 Metric triangle screws
Metric triangular screws have norms as metric normal screws and fine screws. When external cross sections of a metric screw are analyzed, it is observed that the end of the side of the triangle constituting the threads has been curved with a radius of 1/6 of the height of the triangle. This is called the curve of the base of the thread. Curve of the base of the thread has been designed to increase resistance of threads against excessive load. Metric screws are preferred in connections due to these features.

Diameters of Screws
d = D pitch
P Diameter of flank
d2 = D2 Diameter of base of thread
d3 D1 Depth of Thread
h3 H Diameter of borer
3 0,5 2,675 2,387 2,459 0,307 0,271 2,5
4 0,7 3,545 3,141 3,242 0,429 0,271 3,4
5 0,8 4,48 4,019 4,134 0,491 0,433 4,25
6 1 5,35 4,773 4,917 0,613 0,541 5,1
8 1,25 7,188 6,466 6,647 0,767 0,677 6,8
10 1,5 9,026 8,16 8,376 0,92 0,812 8,5
12 1,75 10,863 9,853 10,106 1,074 0,947 10,2
14 2 12,701 11,402 11,688 1,226 1,825 11,9
16 2 14,701 13,546 13,835 1,227 1,083 13,6
20 2,5 18,376 13,933 17,294 1,534 1,353 17
24 3 22,051 20,319 20,752 1,84 1,624 20,4
30 3,5 27,727 25,706 26,211 2,147 1,894 25,5
36 4 33,402 31,93 31,67 2,454 2,165 30,6
42 4,5 39,077 36,479 37,129 2,76 2,436 35,7

2.1.1 Metric fine screws

Metric fine thread screws mean opening a screw with small pitch on a thick diameter. The helix angle is smaller in screws with fine thread when compared with normal screws. As the helix angle of a screw gets smaller, the degree of auto blockage, hence resistance against shocks and force increases. Then, it would not be easy for fine thread screws to be unscrewed easily by themselves. Fine thread screws are used when such features are required. This is the reason why fine screws are used extensively in automobile and airplane industries.

2.2 Whitworth triangular screws

Whitworth screws are produced in 3 norms and measures as normal withworth screws, fine thread whitworth screws, whitworth pipe screws. The top angle of whitworth screws is 55º. The tops of triangles constituting the threads in whitworth screws have been cut off and curved by 17& of the theoretical height of the triangle. The nut of the screw is also made in the same measurements. Theoretically there is no space between nut threads and threads of the screw. For this reason, whitworth screws are screws that prevent leakage. However, when the thread of nuts and screw threads clasp each other in metric screws, small cavities occur at the tip of the threads. Hence, threads clasp each other only from sides. However, threads of nuts and threads of bolts clasp each other totally in whitworth screws. Whitworth screws are used for pipe connections that require non-leakage due to these features. Metric screws however are only used as connection screws.

Diameter in terms of inch
d Section circle of diameter on top of thread
d2 = D2 Diameter of base of thread
( mm )
d1 = D1 Pitch
P  Number of threads
Z Curve
r Thread Height
H1 Cross-section of base of Thread
MMxMM
1"/4 6,35 5,537 4,724 1,27 20 0,174 0,813 17,5
5"/16 7,938 7,034 6,131 1,411 18 0,194 0,904 29,5
3"/8 9,525 8,509 7,492 1,558 16 0,218 1,917 44,1
7"/16 11,119 9,951 8,769 1,814 14 0,249 1,162 60,7
1"/2 12,7 11,345 9,99 2,117 12 0,291 1,355 78,4
5"/8 15,876 14,397 12,918 2,309 11 0,317 1,497 131
3"/4 19,051 17,424 15,798 2,54 10 0,349 1,627 196
7"/8 22,226 20,419 18,611 2,822 9 0,388 1,807 272
1" 25,401 23,368 21,335 3,175 8 0,496 2,033 350
1" x 1"/8 28,578 26,253 23,929 3,629 7 0,498 2,324 450
1" x 1"/4 31,751 29,428 27,104 3,629 7 0,498 2,324 577
1" x 3"/8 34,926 32,215 29,,505 4,233 6 0,581 2,711 684
1" x 1"/2 38,101 35,391 32,68 4,233 6 0,581 2,711 839
1" x 5"/8 41,277 38,024 34,771 5,08 5 0,698 3,253 960
1" x 3"/4 44,452 41,199 37,946 5,08 5 0,698 3,253 1131
1" x 7"/8 47,627 44,012 40,398 5,645 4 x 1/2 0,775 3,614 1282
2" 50,822 47,187 43,573 5,645 4 x 1/2 0,755 3,614 1491

2.2.1 Pipe screw

The screw known as pipe screw in practice is a whitworth triangle screw. This is called pipe screw just because it is has norms and is made for pipe connections. The external cross section of the pipe screw is just like the cross section of a normal screw. However, pitch of elements constituting the threads in pipe screws is smaller than normal pitch screws. Hence, there are more threads in a finger length when compared with a normal screw. A significant characteristics of pipe screws is the fact that its threads are made conic in the ratio of 1/16

Finger Measurement Diameter of Top of Thread
( mm ) Diameter of flank
( mm ) Diameter of base of thread
( mm )
d1 = D1 Pitch
( mm )
P Number of threads
Z Depth of Threads
H1 Curve
r
R 1/8 9,728 9,147 8,566 0,907 28 0,581 0,125
R 1/4 13,157 12,301 11,445 1,337 19 0,856 0,184
R 3/8 16,662 15,806 14,95 1,337 19 0,856 0,184
R 1/2 20,955 19,793 18,631 1,814 14 1,162 0,249
R 5/8 22,911 21,479 20,587 1,814 14 1,162 0,249
R 3/4 26,441 25,279 24,117 1,814 14 1,162 0,249
R 7/8 30,201 29,039 27,877 1,814 14 1,162 0,249
R 1 33,249 31,77 30,291 2,309 11 1,479 0,317
R 1x1/8 37,897 39,418 34,939 2,309 11 1,479 0,317
R 1x1/4 41,91 40,431 38,952 2,309 11 1,479 0,317
R 1x3/8 44,323 42,844 41,365 2,309 11 1,479 0,317
R 1x1/2 47,803 46,324 44,845 2,309 11 1,479 0,317
R 1x3/4 53,746 52,267 50,788 2,309 11 1,479 0,317
R 2 59,614 58,135 56,656 2,309 11 1,479 0,317
R 2x1/4 65,71 64,231 62,752 2,309 11 1,479 0,317
R 2x1/2 75,184 73,705 72,226 2,309 11 1,479 0,317
R 2x3/4 81,534 80,055 78,576 2,309 11 1,479 0,317
R 3 87,884 86,405 84,926 2,309 11 1,479 0,317
R 3x1/4 93,98 92,851 91,022 2,309 11 1,479 0,317
R 3x1/2 100,33 98,851 97,372 2,309 11 1,479 0,317
R 3 x1/4 106,68 105,201 103,722 2,309 11 1,479 0,317
R 4 113,03 111,551 110,072 2,309 11 1,479 0,317
R 4x1/2 125,73 124,251 122,772 2,309 11 1,479 0,317
R 5 138,43 136,951 135,472 2,309 11 1,479 0,317
R 5x1/2 151,13 149,651 148,172 2,309 11 1,479 0,317
R 6 163,83 162,351 160,872 2,309 11 1,479 0,317

2.3 Screws with Multiple Jaws

As the name calls for it, screws with more than one jaw are called screws with multiple jaws.
When a screw with a single jaw is compared with a screw of three jaws, it is observed that the screw with three jaws proceed three times more than the screw with a single jaw in a single revolution.

Screws with multiple jaws are used for systems with low number of revolutions that need to proceed. Shafts of presses with screws, screws of valves, screws of clamps, screws of certain presses, pulling apparatus, and movement adjustments of cameras are screws with multiple jaws. External profiles of movement screws are in the form of squares and trapezoids however, screws with multiple jaw and circular profile can be used in certain mechanisms (clasping shafts of trains).

2.4 Left screws

When screws are unscrewed when they are turned left or right under certain special conditions or when it has to take the block that it carries to the left, it is produced as a left thread screw. Pedal screws of bicycles, the screw on the left of emery rocks fastening the rock on the left, one side of the stretching nuts on the opposite side of the clamps, both jaws of which are movable are made with screws with left thread. LH referring to left hand is pressed on a visible part of screws with left thread to indicate them, there are also circular clogs on corners of left thread nuts.

Left thread screws are tightened by turning towards left, right screws on the other hand are tightened by turning right
The axis of the screw is held perpendicular to the plane of the floor to understand whether a screw is right or left and if the threads of the screw rises towards right it is a screw with right thread and if it rises towards left, then it is a screw with left thread.

3. BOLTS AND NUTS

3.1. BOLTS

Components that connect parts of a machine to each other or connect the trunk of a machine to any other place are called bolts if they are tightened by using a wrench and are called screws if they are tightened by using a screwdriver. When bolts are tightened with a nuts wrench, they clenched with more force. Their size is also greater than screws.

Bolts are generally tightened with nuts. However, screws are screwed on a body.

Bolts and screws can be hand made. However, it would not be possible to meet the needs of the industry in this manner. Furthermore, high labor costs, material consumption causes hand made production of screws to be very expensive. For this reason, bolts and screws are made in special machines from their material automatically by machining. Special machines producing thousands of bolts and screws in an hour were produced for this reason.

All bolts are not used under the same conditions. Some are used under cold and some under heat. Connection has to remain secure under these conditions. For this reason, when bolts are produced, they have to be produced in technical and metrological features that fit the environment.

3.1.1 Bolts and Screws according to their head shape

3.1.1.1 Bolts with Six Angular Heads

Bolts with six angular heads are connection elements that are used most in the machine industry. External forms of bolts are made as normal or fine depending on the features required by the work. The threaded part of the bolt is determined according to the place where it will be used. And it will include sufficient number of threads or will be threaded from one end to the other depending on the kind of work. Any part of a bolt that has been threaded should not be extended by a threading. This is due to the fact that since bolts are opened in automatic machines, the base of the threaded part is not in full screw profile. For that reason, threading opens threads by breaking them. Connection with a bolt with broken threads would not be secure.

3.1.1.2 Cylindrical Headed Countersunk (Allen) Head bolt

When the place where the head of the bolt will be placed is so narrow that an open end wrench cannot be placed or when it is not required that the head of the bolt remains outside, cylindrical headed countersunk (Allen) Head Bolts or Allen screws with smaller bolts are used.

3.1.1.3 Countersink Headed Alien Wrench Bolts

Heads of countersink headed Alien wrench bolts are thinner than bolts with cylindrical head. When it is necessary that the head of the bolt does not remain outside when connecting fine materials, countersunk screws are used.  The countersink on the head of the bolt makes it possible to tighten the hole at the center.

3.1.1.4 Cylindrical Screws with Screw Jaw

Cylindrical screws with screws are used in such small connections that can be screwed and unscrewed with cylindrical screws with screw jar. The parts as thick as sheet iron are connected with cylindrical screws and thicker parts are connected with countersink or lentil counter sunk screws.

3.1.1.5 Screws with Philips Screwdriver jaw

Screws with Philips Screwdriver jaw screw tighter than other screws of the same dimensions. The most important benefit of screws with Philips Screwdriver jaw is the fact that the form of the jaw is not distorted when screwing or unscrewing. As the tightening force is separated into four directions in the jaw of the Philips screwdriver, screwing is made very strongly but the mouth is not distorted. Generally the jaws of Philips screwdrivers are opened with small screws.

3.1.2 Screws according to form of their body

3.1.2.1 Plunges (Screws without head)

Plunges are screws without a handle, which are headed on both sides. Plunges are used in connections that are often screwed and unscrewed. Plunges are tightened strongly in a manner that will remain fixed on the trunk of the machine Once the part to be connected is placed, they are tightened with the nuts to be placed on the plunges. When the parts connected are to be unscrewed, only the nuts are removed. The plunge remains in place. In this way, shape of screws on the main trunk is protected.

3.1.2.2 Flexible Bolts

Flexible bolts are made to prevent physical differences that may occur in the connection with the effect of forces exerting pressure on the connection in axial direction. The diameter of trunk of flexible bolts can become thinner by 10% of base of the thread. The bolt is extended to a certain extent from the part that has been thinned with the effect of the forces exerted on the bolt. When force is removed, the bolt regains its old shape. This is caused by the elasticity of the material of the bolt. No separate security system is needed to prevent flexible bolts from unscrewing. The fact that they have been tightened very strongly and that they are elastic eliminates this problem.

3.1.2.3 Bolts with Tolerant Trunk

Certain machine elements transmitting large momentums are connected with special bolts stoned as surface tolerant. Furthermore, the holes that the bolts pass through are reamed. If elements transmitting large force in this manner cannot be connected with sensitive frameworks in this manner, hence if the hole of the bolt is wide, the bolt will be faced with a sudden large cutting force on the first moment of operation. The life of bolts forced with such abrupt force cuts will be short. They fail unexpectedly and the system undergoes breakdown.

3.1.3 Resistance of Bolts

Bolt materials have to be selected from resistant steel in order for connections made with bolts to be secure. It is requested that the material is resistant to prevent abrasion of threads and breaking away of the base of the thread by extension. Besides, threads of the bolt should clasp through the nuts or if the bolt is screwed into a trunk, it should be screwed minimum at the height of a nut, for this, the thickness of the nut of a bolt is found by multiplying its diameter with 0,8.

3.2 Nuts

Nuts are parts of a bolt and are the element of a machine that fulfills the function of tightening in the connection. Nuts are produced according to the dimensions of the bolts that they will be used with. However, the forms of threads may be in different forms depending on their features of use. The compression force is transmitted to the components connected by head of a bolt and the nut in a connection with bolts. The more the nut is screwed, the more does the bolt try to extend from the bottom of the thread.  Similarly, the threads of nuts are also forced to graze. The threads on which the nuts stand, hence the threads that clasp the bolts carry more force. This force becomes less when approaching the last thread. This indicates that the first threads of the nuts are forced more. The fact that first threads undergo abrasion in nuts that are unscrewed and screwed often proves this.

3.2.1 Types of Nuts

3.2.1.1 Nuts with Six angles

The materials of nuts can generally be made of materials less resistant materials of bolts. The resistance values are written on the nuts just as they are written on the bolts.

3.2.1.2 Nuts with Dome

One side of a nut with dome is closed in the shape of a dome. The reason for this is to provide protection to the external part of the bolt and to also cause a nice appearance.

3.2.1.3 Perforated Nuts

Perforated nuts are used in places that need to be unscrewed and tightened often by hand; for instance moulds and apparatus.

3.2.1.4 Reduction Nuts (Decreasing Diameter)

Reduction nuts are used to decrease pipes with thick diameter to thin diameter. A pipe with thick diameter is inserted on the edge of the nut where a screw is opened and a pipe with thin diameter with its hat shaped edge is installed on the perforated part of the nut.

3.2.1.5 Crown Nut

Crown nut is used when a connection with bolt is requested to be secured with cotter pin. The pin is placed after squeezing the nut well and the connection is completed by bending outwards the parts that remain outside.

3.2.1.6 Butterfly Nuts

They are nuts produced to manually connect and cast loose work moulds and similar apparatus. Butterfly nuts should be tightened and unscrewed only manually, pincers or other similar devices should never be used.

4. Tapping

As it is known, a screw is opened on two separate parts, one known as inner screw = nuts and the other one outer screw= bolts. Inner screws, i.e. nuts are opened with an equipment called guide and external screws, hence bolts are opened with an equipment called tap-wrench or are produced in machines as series production.

4.1 Guides

Guides are made of high quality series steel ( HSS ). Threads of a guide are stoned according to the zero profile of a screw that it belongs to. Sufficient machining space should be provided for cutting well and that are determined with ideal angles. The machining is flat or helix shaped in order for guides to cut and machining to flow easily. Helix guide help cutting in guides of  the machining of which is helix shaped, machining channels also facilitate lubrication and effect cutting. Guides are divided into two in the form of hand guides and machine guides. Manual guides are hand made, machine guides are prepared in machines; for instance, drill, turning and automatic turns.

4.1.1 Hand Guides

Hand guides are generally produced in the form of sets that include three guides in them. Hand guides are made with three channels for soft materials and with four channels for steel type materials. Threads on conic length on the edge of the guide are responsible for cutting in a guide. Threads that come after the conic part are embedded inside the screw and help the axial course of the guide.

4.1.2 Machine Guides

Machine guides are not like hand guides and they comprise of a single part. They are divided into two as helix and flat. Guides with flat channels are for overall holes and helix shaped guides are for blind holes.

4.1.3 Pulling Guide

4.1.3.1 Preparation of the Work

A part of work that will be tapped should first of all be prepared for this transaction in a perfect manner. Boring the hole in appropriate dimensions and opening a countersink of 90 degrees is significant for speeding up the work. The hole is opened according to the diameter of the base of the thread of the nut. The real diameter of real base of thread of all inner screws made is always grater than theoretical diameter. The guide is tightened and broken if the diameters are same. For this reason, when inner screws are made, they are borne according to a larger diameter known as borer diameter instead of the diameter of end of the thread. The bore diameter of a screw is practically calculated by multiplying the diameter of top of the thread by 0,85 or by subtracting the thread from the diameter of the upper part of the thread.

If a hole is to be guided overall, then a countersink of 90 degrees should be opened on both sides of the hole. Countersink provides ease for installation and prevents formation of crust on the jaw of the screw. On the other hand, is screw is to be opened on a thicker material and if the material is to be perforated from one end to the other, there is no need to provide overall guide. This is because guide is quite an expensive set. It should not be used haphazardly to prevent blunting. Furthermore, opening long screws unnecessarily also causes increase in labor costs. For this reason, it is necessary to open a thread to a point as much as the length of the screw that will be used. For this reason, the length on which thread will be opened should be extended in the manner that it will be 1.5 times of the diameter. If tapping will be applied on a blind hole then attention should be paid to keep it as deep as possible.

4.1.3.2 Manual Tapping

The handle should be selected well before anything else during manual tapping. The hole of the handle should conform to the head of the guide and it should not be broken down. Main tap handles are seen in the figure. Tap handle with three holes does not seem to be suitable for small taps. This is due to the fact that one of the handles is longer and the other one is shorter. The tap can be broken if not handled carefully. The perforated parts of tap handles should be hard. Upon failure to conform to this, the holes get wider and the handle cannot be used.

4.1.3.3 The Order of processes to be followed during manual tapping

1, Tap is held parallel to the axis of the hole. It is revolved slowly around its axis and is reached to the work. Attention should be paid for not extending the jaw of the hole.

2. The guide moves approximately three, four threads and revolving is done with two hands and the process with the first tap ends.

3. Second and third taps are also applied in the same manner.

During tapping, the guide is slightly pulled back to break the machining In this manner compression of machining in the tapping channel is prevented. It would not be possible to open a high quality and clean screw with blunt taps. Besides, there is also the danger of breaking for the tap. Therefore, blunt taps have to be used after they have been sharpened. Upon failure to do this, a larger revolving force is required when screwing with a blunt tap. If taps are pulled with much force, it may be broken at once. It is very difficult to take out a tap that has been broken in the hole. Also, the whole work may be faced with failure as a result. Screws should not be pulled with a blunt tap to prevent this. It is necessary to pull and finish if there is no possibility for the machining to be squeezed on the sides of the tap. Because the sharp edges of threads can be broken when pulling back.

4.1.3.4 Pulling out the broken guide

Lack of attention for a moment may cause tap to be broken. In such case the part of the tap that is left in the hole will be taken out. Since the part that is made is produced with much effort, it cannot be considered to leave it aside as scrap. First of all small parts are drawn, moved and taken out to take the part of taps in the hole, then it is chosen as three or four feet (depending on the number of feet of tap). A wrench for removing taps is used. The feet of the wrench is placed on the sided of the tap. The tap is turned on the reverse side and removed.

4.1.3.5 Matters to be taken into consideration during tapping

1.Diameters of base of thread of nuts to be used in connections where fluids such as vapor and gas will not pass will be borne somewhat bigger than their real value. This rule is for normal and fine thread metric and whitworth screws.
2. Attention should be paid to choose correctly the bore that will give the diameter of the base of a thread.
3. When the diameter of the base of a thread is borne, the carrying power of the screw will fall in gray casting materials. Because, when gray casting taps are pulled, the tap will effect as reamer and extends width of the screw to a certain extent. This causes the threads to be weakened to a certain extent.
4. 90 degrees countersink is opened on both sides of the hole to be tapped. The external base of the countersink diameter is opened 2 mm larger.
5.The conic degree of the tap should be chosen at suitable values depending on the hardness of the material to be screwed. The size of the edge conic side should be large, hence it should be maximum 5 degrees.
6. The machining angle of the tap should also conform to the screw material. Taps made for soft materials should not be used for steel materials. Otherwise, the ends of cutting threads break easily.
7. Nitration hardened special taps should be used for gray cast materials. If screws will be opened on numerous casting materials, it would be beneficial to prefer such taps. Because cast materials cause fast abrasion of taps.
8. When tapping, attention should be given for them to be made of HSS steel and that the back of threads is stoned.
9. If the tap is to be pulled in blind hole, the depth of the hole should be the length of the screw + 0,7 x d.
10. The tap should be applied on the full axis of the hole. For this, the perpendicularity of the tap should be checked from a few directions with a t-square at the beginning.
11. The pressure to be exerted on both sides of the tap handle should be equal. Otherwise tapping would be curved.
12. When the tap opens a fat for itself and two or three threads go inside the hole, axial pressure is not needed anymore. It is just necessary to revolve carefully.
13. If the cutting threads on the conic part of the guide are blunt, they will not cut well. The tap will be slogged. The threads on the cylindrical part of the tap are compressed For this reason, blind guides should be sharpened.
14. After moving ahead the second and third taps a few threads manually it is recommended to put it on the tap handle. Otherwise, tapping can be in a wrong manner.
15. Tapping is made in the order of their number. In other words, first one, then two and then three taps are made.
16. Machining by reversing should not be preferred unless mandatory. Because the external sides of the tap break when forced from reverse.
17. Four channel taps are made for steel type materials, three channel taps with larger machining angle are made for soft materials. Taps with three channels should not be used on steel materials by mistake.
18. The handle of the guide should not be broken down or extended. The handle should be adjustable or global.
19. Machining on the base of blind holes should be cleaned one or two times. Otherwise, screws with sufficient depth would not be opened.
20. Lubrication is not used when tapping on materials such as cast, peak, brass and magnesium, which are rough textured and are delicate. All other materials except for these should be lubricated during tapping. Lubrication facilitates cutting during tapping and prevents blinding. It makes the surface of the screw to remain clean.

4.2 Threading

4.2.1 Threads

Threads are sets that are different from taps. Although three taps are used when making a nut by hand, only a single thread is used when making the bolt of a nut. Just like taps, threads are also made from high quality steels ( HSS ) and extra quality steels ( HSSE ). Threads made of extra quality steels ( Emo5V3 ) are made for alloyed cast steel and resistant steel is used for special steel resistant against stainless acids.

The number of cutting jaws range between 3 and 6 depending on the size of the threads. The angle of machining in mouths comprise of the curve constituting the cavity of machining, in other words the curve of the diameter of the curve forming the machining also forms the machining angle.

The jaw share of the thread makes it to grasp the work, this is 60 for brass and 90 for other softer metals. This indicates that screwing to steels with threads made for brass materials is not possible. Threading companies write the symbol of brass (Ms) on threads that they produce for brass in order to prevent such a mistake.

Threading is made in 3 types as closed, slotted and open. Closed type thread opens screws with fixed diameter. Slotted thread can be transformed into an adjustable thread when needed by cutting with a stone at the section of slotting. The screw diameter can be adjusted with open type threads. When the screw pressing on the part of the jaw that is open is tightened, the thread is opened to a certain extend and increases the size of the diameter that it opens. Machining is taken to a container in this adjustment. The screw would be clean and in the exact dimensions when pulling for the second time after leaving free.

4.2.2 Thread Arms

As seen in the figure, threads are used by placing on the thread arm. Thread arms are made of two parts in the form of trunk and arms. The trunk and arms of an ideal thread arm should be made of steel and should be processed clean. It is necessary that the arms are right at the axis of the trunk. Otherwise, establishing control when threading becomes difficult. The length of thread arms should conform to the size of the threads to be used. For this reason, there are thread arms of different sizes.

4.2.3 Preparation of the work to be threaded

There are two significant points in preparation of the work to be threaded. The first one of these is the diameter of the work and the other one is the bevel to be placed on the edge. Just like boring the diameter of the base of the thread when making a nut, similarly the diameter of the part that will be threaded is made somewhat smaller. Similarly, since the base of thread can not be machined from the external diameter, the upper part of the screw comes out to be flat. In this manner the risk for the thread to be broken is eliminated. In the end a clean screw is produced. The second point in preparation of the work is beveling to the edge of the work by 60 degrees. If beveling is made in casual manner on the tip of a screw, jawsing threading becomes difficult.

4.2.4 Pulling Back Threading

Threading should be made just like tapping by transforming slowly with axial pressure. After clasping the two threads, it is turned normally and the process continues. Just as tapping, threading should also not be pulled back. Otherwise, threads may break

4.2.5 Matters to be Taken into Consideration during Threading

1. Normal threading is preferred if the pitch of the screw is smaller than 2 mm. If a screw with pitch grater than 2 mm is to be produced, an open thread, hence an adjustable thread should be preferred.
2. Thread should be sharp, threads should be broken. Otherwise the screw comes out in defected manner.
3. A thread that conforms to the type of the material to be screwed should be chosen.
4. Thread should be cleaned well before placing the handle of the thread.
5. Attention should be given to prevent curves and bends when threading.
6. Equal forces should especially be exerted on both handles of the thread. Otherwise, the thread would be bent and the jaw of the screw would be damaged.
7. The screw should be finished by turning the thread in the same direction.
8. Abscission lubricant should be definitely used when threading.
9. Abscission lubricants are not used when tapping or threading with grey cast, brass, magnesium etc which are fragile and sensitive. Otherwise, fine dust that comes out of the material is mixed with lubricants and a dense liquid is established. This causes the thread and tap to be blinded quickly.

5. Making Screws by lathing

5.1 Making Flat Screws by Lathing

Screw tables by lathing are convenient at various pitches when compared with metric and inch measurement units. The revolving action of the work is transformed to the main shaft with the gear on the main shaft through the work gear shaft. For this reason, the gear shaft is called the thread transformed into work shaft gear.

5.2 Making Left Screw by Lathing

As it is known, a screw is called a left screw if the helix direction of the screw rises towards left. Only the direction of helix is different between left screw and right screw. Other measures are the same. However, opening a right screw on the lathe is easier than the left screw. This is because there is a wider space on the head part for the pen to work when making a right screw and it also extends to the cavity of pen. However, when left screw is opened, the pen moves from the thread cavity of the screw towards right. Since this part is quite narrow in the screws and there is also a rabbet at the head of the screw, the chance for the pen to function correctly at each passing becomes difficult.

5.3 Making Long Screws by Lathing

The shaft is extended when the thread is opened on long shafts while the pen cuts. The pen does not cause machining as the work stretches when normal machining while the pen is close to the regions close to the point. If a few passes are made without noticing, the work would exert pressure on the pen without realizing. The pen would be broken or bent. To prevent this, the screw is placed on the lathe base by a bearing named shaft bearing.

5.4 Making Frontal Screws

When frontal screws are opened, the breadthways support of the car makes a movement of advancement according to the pitch of the screw. This force of support is from the main shaft. Attention should be paid when sharpening pens for frontal screws. Since the threads of screws are in the form of a spiral, the lower part of the pen may rub on the sides of the thread.

Attachment 1

Size
Ww Thread
Form
Type Major
Diameter
mm
d=D Pitch
mm
p Threads
per
inch
tpi Pitch
Diameter
mm
d2=D2 Minor
Diameter
Male Thd.
d3 Thread
Height
H1 Tap
Drill
Diameter
mm

1/16" BSW 1.587 0.423 60 1.315 1.050 0.270 1.15
3/32" BSW 2.381 0.529 48 2.041 1.703 0.338 1.90
1/8" BSW 3.175 0.635 40 2.768 2.362 0.406 2.50
5/32" BSW 3.969 0.793 32 3.459 2.952 0.507 3.20
3/16" BSW 4.762 1.058 24 4.084 3.407 0.677 3.70
7/32" BSW 5.556 1.058 24 4.878 4.201 0.677 4.50
1/4" BSW 6.350 1.270 20 5.537 4.724 0.813 5.10
5/16" BSW 7.938 1.411 18 7.034 6.131 0.904 6.50
3/8" BSW 9.525 1.588 16 8.509 7.492 1.017 7.90
7/16" BSW 11.113 1.814 14 9.951 8.789 1.162 9.20
1/2" BSW 12.700 2.117 12 11.345 9.990 1.355 10.40
5/8" BSW 15.876 2.309 11 14.397 12.918 1.479 13.40
3/4" BSW 19.051 2.540 10 17.424 15.798 1.627 16.25
7/8" BSW 22.226 2.822 9 20.419 18.611 1.807 19.25
1" BSW 25.400 3.175 8 23.368 21.335 2.033 22.00
1 1/8" BSW 28.576 3.629 7 26.253 23.929 2.324 24.50
1 1/4" BSW 31.751 3.629 7 29.428 27.104 2.324 27.25
1 3/8" BSW 34.926 4.233 6 32.215 29.505 2.711 30.25
1 1/2" BSW 38.100 4.233 6 35.391 32.680 2.711 33.50
1 5/8" BSW 41.277 5.080 5 38.024 34.771 3.253 35.50
1 3/4" BSW 44.452 5.080 5 41.199 37.946 3.253 38.50
1 7/8" BSW 47.627 5.645 4 1/2 44.012 40.398 3.614 41.25
2" BSW 50.802 5.645 4 1/2 47.187 43.573 3.614 44.50
2 1/4" BSW 57.152 6.350 4 53.086 49.020 4.066 50.00
2 1/2" BSW 63.502 6.350 4 59.436 55.370 4.066 56.00
2 3/4" BSW 69.853 7.257 3 1/2 65.205 60.558 4.647 61.50
3" BSW 76.203 7.257 3 1/2 71.556 66.909 4.647 68.00
3 1/4" BSW 82.553 7.816 3 1/4 77.548 72.544 5.005 73.75
3 1/2" BSW 88.903 7.816 3 1/4 83.899 78.894 5.005 80.00
3 3/4" BSW 95.254 8.467 3 89.832 84.410 5.422 85.50
4" BSW 101.604 8.467 3 96.182 90.760 5.422 92.00
4 1/4" BSW 107.954 8.835 2 7/8 102.297 96.639 5.657 98.00
4 1/2" BSW 114.304 8.835 2 7/8 108.647 102.990 5.657 104.20
4 3/4" BSW 120.665 9.237 2 3/4 114.740 108.625 5.915 110.00
5" BSW 127.005 9.237 2 3/4 121.090 115.176 5.915 116.50
5 1/4" BSW 133.355 9.677 2 5/8 127.159 120.963 6.196 122.50
5 1/2" BSW 139.705 9.677 2 5/8 133.509 127.313 6.196 128.50
5 3/4" BSW 146.055 10.160 2 1/2 139.549 133.043 6.506 134.50
6" BSW 152.406 10.160 2 1/2 145.900 139.394 6.506 141.00
Attachment 2

B1.N-R
M .8-16 (5/16" - 5/8")

 

VABS SCREW FRICTION APPARATUS CAPACITIES

METRIC ISO WHITWORTH UNIFIED
NORMAL FINE NORMAL(BSW) FINE(BSF) UNC UNF
Screw diameter mm Pitch
mm Screw diameter mm Pitch
mm Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch
M8 1.25 M8 1 5/16 18 5/16 22 5/16 18 5/16 24
M9 1.25 M9 1 3/8 16 3/8 20 3/8 16 3/8 24
M10 1.5 M10 1.25 7/16 14 7/16 18 7/16 14 7/16 20
M11 1.5 M12 1.25 1/2 12 1/2 16 1/2 13 1/2 20
M12 1.75 M12 1.5 9/16 12 9/16 16 9/16 12
M14 1.75 M14 1.5 5/8 11 5/8 14 5/8 11
M16 2

Attachment 3

VABS SCREW FRICTION APPARATUS CAPACITIES
METRIC ISO WHITWORTH - UNIFIED WHITWORTH
FINE FINE BSF-UNF BSF-UNF BSF-UNF BSF-UNF BSP
Screw diameter mm Pitch
mm Screw diameter mm Pitch
mm Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter
Pitch
M8
M10 0.5 M14
M16 1.25 5/16 40 1/2
9/16 32 3/4* 26 1/2 20 R 1/8 - 28
M8
M10 0.75 M16
M18* 1.5 5/16
3/8 36 9/16
5/8 32 7/16
1/2 24 9/16
5/8 20 R 1/4 - 19
M10
M12 0.75 M18*
M20* 1.5 3/8
7/16 36 7/16
1/2 28 1/2
9/16 24 11/16
3/4* 20 R 3/8 - 19
M10
M12 1 M20*
M22* 1.5 7/16
1/2 36 1/2
9/16 28 9/16
5/8 24 9/16
5/8 18
M12
M14 1 1/2
9/16 36 9/16
5/8 28 3/4* 24 3/4* 16
M14
M16 1 5/16
3/8 32 7/16
1/2 26 1/2
9/16 22 3/4* 14
M16
M18* 1 3/8
7/16 32 1/2
9/16 26 9/16
5/8 22
M18*
M20* 1 7/16
1/2 32 9/16
5/8 26 3/4* 22

Attachment 4
C2
M .16-32 (5/8" - 1 1/4")

VABS SCREW FRICTION APPARATUS CAPACITIES
METRIC ISO WHITWORTH UNIFIED WHITWORTH
NORMAL FINE NORMAL(BSW) FINE(BSF) UNC UNF BSP
Screw diameter mm Pitch
mm Screw diameter mm Pitch
mm Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter
Pitch
M14
M16 2 M14
M16 1.5 9/16 12 5/8
11/16 14 9/16 12 9/16
5/8 18 R 3/8 - 19
M18
M20 2.5 M16
M18 1.5 5/8
11/16 11 3/4
13/16 12 5/8 11 3/4 16 R 1/2 - 14
M20
M22 2.5 M18
M20 2 3/4
13/16 10 7/8
15/16 11 3/4 10 7/8 14 R 5/8 - 14
M24
M27 3 M22
M24 2 7/8
15/16 9 1 10 7/8 9 1 12
M30 3.5 1 8 1 1/8 9 1 8
1 1/8 7 1 1/8 7

Attachment 5

A1
M .5-8 (3/16" - 5/16")
VABS SCREW FRICTION APPARATUS CAPACITIES

METRIC ISO WHITWORTH UNIFIED
NORMAL FINE NORMAL(BSW) FINE(BSF) UNC UNF
Screw diameter mm Pitch
mm Screw diameter mm Pitch
mm Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch Screw diameter inch Pitch
inch
M5 0.8 M6 0.75 7/32 24 7/32 28 NO.12 24 N0.12 28
M6 1 M7 0.75 1/4 20 1/4 26 1/4 20 1/4 28
M7 1 M8 1 5/16 18 9/32 26 5/16 18 5/16 24
M8 1.25 5/16 22

Attachment 6

B1.N-R
M 8-16 (5/16" - 5/8")

B1.N.İ-R
M 8-16 (5/16" - 5/8")