ASME B18.3 Hexagon socket head cap screws
ASME B18.3 Dimensions of Hexagon Socket Head Cap Screw
| Nominal Size (Basic Screw Diameter) [Note (7)] |
Body Diameter, D [Notes (8) and (9)] |
Head Diameter, A [Notes (10)] |
Head Height, H |
Maximum Chamfer or Radius, C [Note (11)] |
Nominal Hexagon Socket Size, J [Note(12)] |
Minimum Key Engagement, T |
Minimum Wall Thickness, G |
Minimum Chamfer or Radius, K [Note (13)] |
|||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Max | Min | Max | Min | Max | Min | ||||||||
| 0 | (0.0600) | 0.0600 | 0.0568 | 0.096 | 0.091 | 0.060 | 0.057 | 0.004 | ... | 0.050 | 0.025 | 0.020 | 0.007 |
| 1 | (0.0730) | 0.0730 | 0.0695 | 0.118 | 0.112 | 0.073 | 0.070 | 0.005 | 1/16 | 0.062 | 0.031 | 0.025 | 0.007 |
| 2 | (0.0860) | 0.0860 | 0.0822 | 0.140 | 0.134 | 0.086 | 0.083 | 0.008 | 5/64 | 0.078 | 0.038 | 0.029 | 0.007 |
| 3 | (0.0990) | 0.0990 | 0.0949 | 0.161 | 0.154 | 0.099 | 0.095 | 0.008 | 5/64 | 0.078 | 0.044 | 0.034 | 0.007 |
| 4 | (0.1120) | 0.1120 | 0.1075 | 0.183 | 0.176 | 0.112 | 0.108 | 0.009 | 3/32 | 0.094 | 0.051 | 0.038 | 0.008 |
| 5 | (0.1250) | 0.1250 | 0.1202 | 0.205 | 0.198 | 0.125 | 0.121 | 0.012 | 3/32 | 0.094 | 0.057 | 0.043 | 0.008 |
| 6 | (0.1380) | 0.1380 | 0.1329 | 0.226 | 0.218 | 0.138 | 0.134 | 0.013 | 7/64 | 0.109 | 0.064 | 0.047 | 0.008 |
| 8 | (0.1640) | 0.1640 | 0.1585 | 0.270 | 0.262 | 0.164 | 0.159 | 0.014 | 9/64 | 0.141 | 0.077 | 0.056 | 0.008 |
| 10 | (0.1900) | 0.1900 | 0.1840 | 0.312 | 0.303 | 0.190 | 0.185 | 0.018 | 5/32 | 0.156 | 0.090 | 0.065 | 0.008 |
| 12 | (0.2160) | 0.2160 | 0.2095 | 0.324 | 0.314 | 0.216 | 0.210 | 0.022 | 5/12 | 0.156 | 0.103 | 0.082 | 0.010 |
| 1/4 | (0.2500) | 0.2500 | 0.2435 | 0.375 | 0.365 | 0.250 | 0.244 | 0.025 | 3/16 | 0.188 | 0.120 | 0.095 | 0.010 |
| 5/16 | (0.3125) | 0.3125 | 0.3053 | 0.469 | 0.457 | 0.312 | 0.306 | 0.033 | 1/4 | 0.250 | 0.151 | 0.143 | 0.010 |
| 3/8 | (0.3750) | 0.3750 | 0.3678 | 0.562 | 0.550 | 0.375 | 0.368 | 0.040 | 5/16 | 0.312 | 0.182 | 0.143 | 0.010 |
| 7/16 | (0.4375) | 0.4375 | 0.4294 | 0.656 | 0.642 | 0.438 | 0.430 | 0.047 | 3/8 | 0.375 | 0.213 | 0.166 | 0.015 |
| 1/2 | (0.5000) | 0.5000 | 0.4919 | 0.750 | 0.735 | 0.500 | 0.492 | 0.055 | 3/8 | 0.375 | 0.245 | 0.190 | 0.015 |
| 9/16 | (0.5625) | 0.5625 | 0.5538 | 0.843 | 0.827 | 0.562 | 0.554 | 0.62 | 7/16 | 0.437 | 0.276 | 0.214 | 0.015 |
| 5/8 | (0.6250) | 0.6250 | 0.6163 | 0.938 | 0.914 | 0.625 | 0.616 | 0.070 | 1/2 | 0.500 | 0.307 | 0.238 | 0.015 |
| 3/4 | (0.7500) | 0.7500 | 0.7406 | 1.125 | 1.107 | 0.750 | 0.740 | 0.085 | 5/8 | 0.625 | 0.370 | 0.285 | 0.015 |
| 7/8 | (0.8750) | 0.8750 | 0.8647 | 1.312 | 1.291 | 0.875 | 0.864 | 0.100 | 3/4 | 0.750 | 0.432 | 0.333 | 0.020 |
| 1 | (1.0000) | 1.0000 | 0.9886 | 1.500 | 1.479 | 1.000 | 0.988 | 0.114 | 3/4 | 0.750 | 0.495 | 0.380 | 0.020 |
| 1 1/8 | (1.1250) | 1.1250 | 1.1086 | 1.688 | 1.665 | 1.125 | 1.111 | 0.129 | 7/8 | 0.875 | 0.557 | 0.428 | 0.020 |
| 1 1/4 | (1.2500) | 1.2500 | 1.2336 | 1.875 | 1.852 | 1.250 | 1.236 | 0.144 | 7/8 | 0.875 | 0.620 | 0.475 | 0.020 |
| 1 3/8 | (1.3750) | 1.3750 | 1.3568 | 2.062 | 2.038 | 1.375 | 1.360 | 0.160 | 1 | 1.000 | 0.682 | 0.523 | 0.020 |
| 1 1/2 | (1.5000) | 1.5000 | 1.4818 | 2.250 | 2.224 | 1.500 | 1.485 | 0.176 | 1 | 1.000 | 0.745 | 0.570 | 0.020 |
| 1 3/4 | (1.7500) | 1.7500 | 1.7295 | 2.625 | 2.597 | 1.750 | 1.734 | 0.207 | 1 1/4 | 1.250 | 0.870 | 0.665 | 0.020 |
| 2 | (2.0000) | 2.0000 | 1.9780 | 3.000 | 2.970 | 2.000 | 1.983 | 0.238 | 1 1/2 | 1.500 | 0.995 | 0.760 | 0.020 |
| 2 1/4 | 2.2500 | 2.2500 | 2.2280 | 3.375 | 3.344 | 2.250 | 2.232 | 0.269 | 1 3/4 | 1.750 | 1.120 | 0.855 | 0.036 |
| 2 1/2 | 2.5000 | 2.5000 | 2.4762 | 3.750 | 3.717 | 2.500 | 2.481 | 0.300 | 1 3/4 | 1.750 | 1.245 | 0.950 | 0.036 |
| 2 3/4 | (2.7500) | 2.7500 | 2.7262 | 4.125 | 4.090 | 2.750 | 2.730 | 0.332 | 2 | 2.000 | 1.370 | 1.045 | 0.036 |
| 3 | (3.0000) | 3.0000 | 2.9762 | 4.500 | 4.464 | 3.000 | 2.979 | 0.363 | 2 1/4 | 2.250 | 1.495 | 1.140 | 0.036 |
| 3 1/4 | 3.2500 | 3.2500 | 3.2262 | 4.875 | 4.837 | 3.250 | 3.228 | 0.394 | 2 1/4 | 2.250 | 1.620 | 1.235 | 0.036 |
| 3 1/2 | 3.5000 | 3.5000 | 3.4762 | 5.250 | 5.211 | 3.500 | 3.478 | 0.426 | 2 3/4 | 2.750 | 1.745 | 1.330 | 0.036 |
| 3 3/4 | 3.7500 | 3.7500 | 3.7262 | 5.625 | 5.584 | 3.750 | 2.727 | 0.458 | 2 3/4 | 2.750 | 1.870 | 1.425 | 0.036 |
| 4 | (4.0000) | 4.0000 | 3.9762 | 6.000 | 5.958 | 4.000 | 3.976 | 0.489 | 3 | 3.000 | 1.995 | 1.520 | 0.036 |
GENERAl NOTE: For additional requirements, refer to Notes (14) through (21), and also section 2, General Data, at the beginning of this Standards.
NOTES:
(1) Length. The length of the screw shall be measured parallel to the axis of the screw from the plane of
the bearing surface under the head to the plane of the flat of the point. The portion of the screw
contained within dimension L is commonly called the shank. The basic length dimension on the product shall
be the nominal length expressed as a two-placed decimal.
(2) Standard Lengths. Standard length increments for socket head cap screws shall be as tabulated below.
| Nominal Screw Size, in. | Nominal Screw Length, in. | Standard Length Increment |
|---|---|---|
| 0 to 1.00, incl. | 0.13 through 0.25 0.25 through 1.00 1.00 through 3.50 3.500 through 7.00 7.00 through 10.00 |
0.06 0.13 0.25 0.50 1.00 |
| Over 1.00 | 1.00 through 7.00 7.00 through 10.00 Over 10.00 |
0.50 1.00 2.00 |
(3) Length Tolerances. The allowable tolerance on length shall be as tablutad below.
| Nominal Screw Size, Tolerance on Lengths | ||||
|---|---|---|---|---|
| Nominal Screw Length, in. | 0 Through 3/8, Incl. | 7/16 Through 3/4 Incl. | 7/8 Through 1 1/2 Incl. | Over 1 1/2 |
| Up to 1.00, Incl. | -0.03 | -0.03 | -0.05 | ... |
| Over 1.00 to 2.50, Incl. | -0.04 | -0.06 | -0.10 | -0.18 |
| Over 2.5 to 6.00, Incl. | -0.06 | -0.08 | -0.14 | -0.20 |
| Over 6.00 | -0.12 | -0.12 | -0.20 | -0.24 |
(4) Thread Length LT. The length of thread shall be measured, parallel to the axis of the screw, from the extreme point to the last complete (full-form) thread. The thread length on socket head cap screws shall be as defined by Table 4 and notes thereto.
(5) Grip Gaging Length LG. Grip gaging length is the distance, measured parallel to the axis of the screw, from the bearing surface of the head to the first complete (full-form) thread under the head (see Table 4).
(6) Body Length LB. Body length is the length, measured parallel to the axis of the screw, of the unthreaded portion of the shank (see Table 4).
(7) Fillet. For all lengths of screws, the form of the underhead fillet shall be optional, as depicted in the illustration above Tables 2 and 3, provided it is a smooth and continuous concave curve fairing into the bearing surface of the head, and the screw shank is within the envelope established by the limits for fillet extension, length, and juncture radius specified in Tables 2 and 3.
(8) Screw Point Chamfer. The point shall be flat or slightly concave and chamfered. The plane of the point shall be approximately normal to the axis of the screw. The chamfer shall extend slightly below the root of the thread, and the edge between the flat and chamfer may be slightly rounded. The included angle of the point should be approximately 90 deg. Chamfering of the screw sizes up to and including size 8 (0.164 in.) and lengths below 0.75d shall be optional.
(9) Nominal Size. Where specifying nominal size in decimals, zeros preceding decimal and in the fourth decimal place shall be omitted.
(10) Head Diameter. Heads may be plain or knurled at the option of the manufacturer, unless specified otherwise by the customer. For knurled screws, the maximum head diameter shall be measured across the tops of the knurl, and the minimum head diameter shall be the diameter of the unknurled portion or the diameter across the tops of the knurl for those screws not having an unknurled portion, just above the radius or chamfer at the bottom edge of the head.
(11) Head Chamfer. The top of the head shall be flat. The intersection of the top of the head and the side of the head may be chamfered or radiused within the limits of C, at the manufacturer’s option.