Cap screws are a versatile type of fastener commonly used in various industries. They typically feature internal or external socket drive heads, with different shapes depending on the type. Below the head, they have a fully or partially threaded shaft with a beveled end. These screws are widely used in machinery, automotive, and industrial manufacturing due to their high yield strength and durability.
Table of contents
Different Types of Cap Screws and Their Applications
Mechanical Properties and Grades of Socket Head Cap Screws
ASTM Standards of Cap Screws
Socket Cap Screw Sizes as per ASME B18.3
Hexagon Socket Head Screws Size Chart (BS 2470)
Button Head Cap Screws Dimension
Recommended Tightening Torque for Button Head Screws
Advantages of Using Cap Screws in Machine Parts and Clamping
How To Measure An Allen Head Socket Cap Bolt
Shank and Thread Length Measurements for Allen Head Cap Bolts
Torque Specs For Socket Head Cap Screws
Cap Screw Applications
Knurled Head Cap Screws Certification
Cap Screws Metric DIN and ISO Standards
Cap Screws vs Socket Screws
Manufacturing Process of Socket Head Cap Screws
Different Types of Cap Screws and Their Applications
Type of Cap Screw
Â
Head Shape
Drive Types
Application
Flat Head Cap Screws
Countersunk
Hex or Socket
Used in applications requiring flush surfaces, countersunk holes
Hex Head Cap Screws
Hexagonal
Hex or Socket
Heavy machinery, structural applications
Socket Head Cap Screws
Cylindrical
Hex Socket
Precision applications, where space is limited
Button Head Cap Screws
Rounded
Hex or Socket
Where a lower profile is needed, aesthetic purposes
Pan Head Cap Screws
Rounded with a flat underside
Hex or Socket
General-purpose, where a large bearing surface is needed
Slotted Hex Cap Screws
Hexagonal
Slotted or Hex
Where the ability to adjust with a slotted screwdriver is desired
Torx Cap Screws
Star-shaped
Torx
High-torque applications
Low Head Socket Cap Screws
Low-profile cylindrical
Hex Socket
For applications with limited vertical space
Hex Flange Cap Screws
Hexagonal with a flange
Hex or Socket
Automotive and machinery applications
Tri-Wing Cap Screws
Triangular winged
Tri-Wing
Security applications
Flat Head Cap Screws are manufactured as per ISO 4762 standard
Mechanical Properties and Grades of Socket Head Cap Screws
Grade
Strength
Tensile Strength (MPa)
Yield Strength (MPa)
Equivalent SAE Grade
8.8
Medium strength
800
640
5
10.9
High Strength
1000
900
8
12.9
Very High Strength
1200
1080
9
ASTM Standards of Cap Screws
ASTM F835 (Alloy Steel Flat Countersunk and Socket Button Head Cap)
ASTM F912M (Alloy Steel Socket Set Screws (Metric))
ASTM F912 (Alloy Steel Socket Set Screws)
ASTM F837M (SS Socket Head Cap Screws (Metric))
ASTM F837 (SS Socket Head Cap Screws)
Round socket head screws are available in a wide range of sizes
Also known as round head cap screws or circle head screws, these fasteners are extremely useful and serve many different advantages. Below are some areas where they are commonly used.
They are often used to assemble electronic components. They are very tough and can also be used as security fasteners. Without the right tools, it can be difficult to install and remove them.
Construction: These screws are easily available, cost-effective, and offer good value for money, making them popular for general construction purposes.
Carpentry: They are easy to use, durable, and not too hard to drill into, which makes them ideal for woodworking tasks.
Fastening thin materials: Due to their unique shape and nearly flat tops, they are perfect for fastening thin materials to other types of material.
Socket Cap Screw Sizes as per ASME B18.3
Thread Size
0
1
2
3
4
5
6
8
10
01/4
5/16
03/8
7/16
01/2
05/8
03/4
07/8
1
T.P.I UNF
80
72
64
56
48
44
40
36
32
28
24
24
20
20
18
16
14
12
T.P.I UNC
Â
64
56
48
40
40
32
32
24
20
18
16
14
13
11
10
9
8
Head Dia (Max) A
0.096
0.118
0.14
0.161
0.183
0.205
0.226
0.27
0.312
0.375
0.469
0.562
0.656
0.75
0.938
1.125
1.312
1.5
Key Engagement (Min) T
0.025
0.031
0.038
0.044
0.051
0.057
0.064
0.077
0.09
0.12
0.151
0.182
0.213
0.245
0.307
0.37
0.432
0.495
Head Height (Max) H
0.06
0.073
0.086
0.099
0.112
0.125
0.138
0.164
0.19
0.25
0.312
0.375
0.438
0.5
0.625
0.75
0.875
1
Key Size J
0.05
1/16
5/64
5/64
3/32
3/32
7/64
9/64
5/32
3/16
01/4
5/16
03/8
03/8
01/2
05/8
03/4
03/4
Thread Length (Max)
0.62
0.77
0.8
0.83
0.99
1
1.05
1.19
1.27
1.5
1.71
1.94
2.17
2.38
2.82
3.25
3.69
4.12
Thread Length (Min)
0.5
0.62
0.62
0.62
0.75
0.75
0.75
0.88
0.88
1
1.12
1.25
1.38
1.5
1.75
2
2.25
2.5
Hexagon Socket Head Screws Size Chart (BS 2470)
Nominal size and thread dia d
Â
0
2
1
3
5
4
6
10
8
12
5/165/16
1/41/4
3/83/8
43467
43593
7/167/16
43528
43654
43528
1
1.1/4
1.1/8
1.3/8
1.3/4
1.1/2
2
Head dia dk
max.max.
0.096
0.14
0.118
0.161
0.205
0.183
0.226
5/165/16
0.27
0.343
7/167/16
3/83/8
9/169/16
43528
0.812
5/85/8
43654
1.1/8
1
1.5/16
1.75
1.5
1.875
2.5
2
2.75
min.min.
0.093
0.136
0.114
0.157
0.2
0.178
0.221
0.306
0.265
0.332
0.429
0.367
0.553
0.739
0.795
0.615
0.863
1.111
0.987
1.297
Â
Â
Â
Â
Â
Â
Pitch of thread
UNC
—
56
64
48
40
40
32
24
32
24
18
20
16
13
12
14
11
9
10
8
7
7
6
5
6
4.1/2
UNF
8000%
6400%
7200%
5600%
4400%
4800%
4000%
3200%
3600%
2800%
2400%
2800%
2400%
2000%
1800%
2000%
1800%
1400%
1600%
14-Dec
1200%
1200%
1200%
–
1200.00%
–
Thread length b
min.min.
0.5
0.625
0.625
0.625
0.75
0.75
0.75
0.875
0.875
0.875
1.125
1
1.25
1.5
1.625
1.375
1.75
2.25
2
2.5
Â
Â
Â
Â
Â
Dia of unthreaded shank dw
max.max.
0.6
0.086
0.073
0.099
0.125
0.112
0.138
0.19
0.164
0.216
0.3125
0.25
0.375
0.5
0.5625
0.4375
0.625
0.875
0.75
1
1.25
1.125
1.375
1.75
1.5
2
min.min.
0.0568
0.0822
0.0695
0.0949
0.1202
0.1075
0.1329
0.184
0.1585
0.21
0.3053
0.2435
0.3678
0.4919
0.554
0.4294
0.6163
0.8647
0.7406
0.98861
1.2336
1.1086
1.3568
1.7295
1.4818
1.978
Width across flats s
nom.nom.
0.05
1/161/16
0.05
5/645/64
3/323/32
5/645/64
3/323/32
5/325/32
1/81/8
5/325/32
7/327/32
3/163/16
5/165/16
43532
43532
5/165/16
43467
43724
43724
43593
43528
43528
43528
1.1/4
1
1.3/8
Thickness of head k
max.max.
0.06
0.086
0.073
0.099
0.125
0.112
0.138
0.19
0.164
0.216
5/165/16
1/41/4
3/83/8
43467
0.562
7/167/16
43593
43654
43528
1
1.25
1.125
1.375
1.75
1.5
2
min.min.
0.057
0.083
0.07
0.095
0.121
0.108
0.134
0.185
0.159
0.201
0.306
0.233
0.368
0.492
0.553
0.43
0.616
0.864
0.74
0.988
1.236
1.111
1.36
1.734
1.485
1.983
Radius under head r
max.max.
0.007
0.008
0.007
0.008
0.01
0.009
0.01
0.014
0.012
0.014
0.017
0.014
0.02
0.026
0.03
0.023
0.032
0.044
0.039
0.05
Â
Â
Â
Â
Â
Â
min.min.
0.003
0.004
0.003
0.004
0.006
0.005
0.006
0.009
0.007
0.009
0.012
0.009
0.015
0.02
0.022
0.018
0.024
0.034
0.03
0.04
Â
Â
Â
Â
Â
Â
Wall thickness w
min.min.
0.019
0.028
0.023
0.032
0.04
0.036
0.044
0.061
0.052
0.074
0.1
0.08
0.12
0.16
0.18
0.14
0.2
0.28
0.24
0.32
0.475
0.428
0.523
0.665
0.57
0.76
Hex socket depth t
min.min.
0.025
0.038
0.031
0.044
0.057
0.051
0.064
0.09
0.077
0.11
0.151
0.12
0.182
0.245
0.276
0.213
0.307
0.432
0.37
0.495
0.62
0.557
0.682
0.87
0.745
0.995
Check dimensions and tensile strength of button head cap screws
It has the similar shape of a pan head with a socket driver. It is manufactured for fastening applications, but doesn’t have the strength like standard socket screws. The socket driver is perfect for low withdrawal applications that require a large clamping face.
Moreover, the button head socket drive gives higher strength than a standard Phillips, allowing fitting in tight spaces. It has a low domed head with a broader bearing surface, offering a finished look. It is ideal when an accurate appearance is required.
