ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws

ASME B18.3 Hexagon Socket Flat Countersunk Head Cap Screws

ASME B18.3 Dimensions of Hexagon Socket Flat Countersunk Head Cap Screw

Nominal Size
(Basic Screw
Diameter)		 Body
Diameter, D		 Head
Diameter, A		 Reference
Head
Height, H		 Protrusion
Gage
Diameter, G		 Protrusion
p		 Nominal
Hexagon
Socket
Size, J		 Minimum
Key
Engagement, T		 Maximum
Fillet
Transition
Diameter, F
Max Min Max Min Max. Min Max. Min
0 (0.0600) 0.0600 0.0568 0.138 0.117 0.044 0.078 0.077 0.044 0.026 ... 0.035 0.025 0.072
1 (0.0730) 0.0730 0.0695 0.168 0.143 0.054 0.101 0.100 0.048 0.028 ... 0.050 0.031 0.089
2 (0.0860) 0.0860 0.0822 0.197 0.168 0.064 0.124 0.123 0.051 0.031 ... 0.050 0.038 0.106
3 (0.0990) 0.0990 0.0949 0.226 0.193 0.073 0.148 0.147 0.054 0.033 1/16 0.062 0.044 0.119
4 (0.1120) 0.1120 0.1075 0.255 0.218 0.083 0.172 0.171 0.057 0.036 1/16 0.062 0.055 0.136
5 (0.1250) 0.1250 0.1202 0.281 0.240 0.090 0.196 0.195 0.059 0.037 5/64 0.078 0.061 0.153
6 (0.1380) 0.1380 0.1329 0.307 0.263 0.097 0.220 0.219 0.060 0.037 5/64 0.078 0.066 0.168
8 (0.1640) 0.1640 0.1585 0.359 0.311 0.112 0.267 0.266 0.063 0.039 3/32 0.094 0.076 0.194
10 (0.1900) 0.1900 0.1840 0.411 0.359 0.127 0.313 0.312 0.066 0.041 1/8 0.125 0.087 0.220
12 (0.2158) 0.2158 0.2102 0.450 0.410 0.135 0.360 0.359 0.069 0.042 1/8 0.125 0.094 0.246
1/4 (0.2500) 0.2500 0.2435 0.531 0.480 0.161 0.424 0.423 0.072 0.043 5/32 0.156 0.111 0.280
5/16 (0.3125) 0.3125 0.3053 0.656 0.600 0.198 0.539 0.538 0.078 0.047 3/16 0.188 0.135 0.343
3/8 (0.3750) 0.3750 0.3678 0.781 0.720 0.234 0.653 0.652 0.088 0.050 7/32 0.219 0.159 0.405
7/16 (0.4375) 0.4375 0.4294 0.844 0.781 0.234 0.690 0.689 0.104 0.063 1/4 0.250 0.159 0.468
1/2 (0.5000) 0.5000 0.4919 0.938 0.872 0.251 0.739 0.738 0.131 0.087 5/16 0.312 0.172 0.530
5/8 (0.6250) 0.6250 0.6163 1.188 1.112 0.324 0.962 0.961 0.146 0.096 3/8 0.375 0.220 0.655
3/4 (0.7500) 0.7500 0.7406 1.438 1.355 0.396 1.186 1.185 0.170 0.105 1/2 0.500 0.220 0.780
7/8 (0.8750) 0.8750 0.8647 1.688 1.604 0.468 1.411 1.410 0.165 0.118 9/16 0.562 0.248 0.905
1 (1.0000) 1.0000 0.9886 1.938 1.841 0.540 1.635 1.634 0.181 0.130 5/8 0.625 0.297 1.030
1 1/8 (1.1250) 1.1250 1.1086 2.188 2.079 0.611 1.859 1.858 0.196 0.140 3/4 0.750 0.325 1.187
1 1/4 (1.2500) 1.2500 1.2336 2.438 2.316 0.683 2.083 2.082 0.212 0.150 7/8 0.875 0.358 1.312
1 3/8 (1.3750) 1.3750 1.3568 2.688 2.553 0.755 2.306 2.305 0.228 0.162 7/8 0.875 0.402 1.437
1 1/2 (1.5000) 1.5000 1.4818 2.938 2.791 0.827 2.530 2.529 0.243 0.173 1 1.000 0.435 1.562

GENERAL NOTE: For additional requirements, refers to Notes (8) through (19) and section 2, General Dat, of this standard.

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 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) Grip Gaging Length LGH. 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 10).

(5) Body Length LBH. Body length is the length, measured parallel to the axis of the screw, of the unthreaded portion of the shank (see Table 10).

(6 )Thread Length LT. The length of the thread shall be measured, parallel to the axis of the screw, from the extreme point to the last complete (full-form) thread. Thread length, on socket flat countersunk head cap screws, shall be as defined by Table 9 and notes thereto.

(7) 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 1.5d shall be optional.

(8) Nominal Size. Where specifying nominal size in decimals, zeros preceding decimal and in the fourth decimal place shall be omitted.

(9) Body. The term body refers to the unthreaded cylindrical portion of the shank for those screws not threaded to the head.

(10) Fillet. A fillet between the conical bearing surface of the head and the shank (body) of the screw is allowable to the maximum F value (Table 8).

(11) Head Diameter. Maximum sharp values under column A are theoretical values only, as it is not practical to make the edges of the head sharp. The maximum sharp value represents the exact diameter of the hole countersunk to exactly 82 deg, in which a screw having maximum head size will fit flush.

(12) Head Height. Tabulated values for head height are given for reference only and are calculated to the maximum formulation.

(13) Protrusion. Suitability of socket flat countersunk head cap screws for application in countersinks designed to the principal dimensions of the screws shall be determined by use of a protrusion gage. The protrusion limits shown shall apply only when the gaging diameter is exactly as indicated with the gaging edge of a sharpness obtained by lapping the hole and the top surface of the gage. The top of the head shall be flat within the limits of the protrusion tolerance. See Mandatory Appendix II for gaging details.

(14) See Table 18 for hexagon socket dimensions and Mandatory Appendix I for gaging of hexagon sockets.