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    2. ASME B18.3

    ASME B18.3 Socket Head Cap Screws Dimensions and Specifications

    Dimensions for Socket Head Cap Screws and Allen Bolts

    ASME B18.3 standard defines the dimensions and specifications for socket head cap screws, also known as Allen bolts, widely used in precision machinery and high-strength assemblies. It covers head configurations, socket dimensions, thread lengths, and tolerances. Here, you will find complete ASME B18.3 socket head cap screw dimensions, technical tables, and sizing information for engineering applications.

    Inch-series socket head cap screws per ASME B18.3 use an internal hex drive (Allen-key engagement) instead of an external wrenching head, making them the fastener of choice for recessed pockets, precision-machined assemblies, machine-tool fixturing, and counterbored mounting. Available 1/4-inch through 4-inch diameter in ASTM A193 Grade B8 304 stainless for corrosion-resistant precision applications. Companion nut for through-bolt usage: ASTM A194 Grade 8.

    HEXAGON SOCKET HEAD CAP SCREW INCH THREAD

    ASME B18.3 Dimensional Tables for ASTM A193 B8 Socket Head Cap Screws

    ASME B18.3 Hexagon Socket Head Cap Screw Dimensions (Inch)

    Nominal Size Basic Screw Diameter Body Diameter, D Head Diameter, A Head Height, H Maximum Chamfer or Radius, C Nominal Hexagon Socket Size, J Socket Width Across Flats, J Minimum Key Engagement, T Minimum Wall Thickness, G Maximum Chamfer or Radius, K Fillet Juncture Diameter, F
    Max. Min. Max. Min. Max. Min. Nom. Dec. Max. Min. Max. Min.
    #0 0.0600 0.0600 0.0568 0.096 0.091 0.060 0.057 0.004 ... 0.050 0.0510 0.0500 0.025 0.020 0.007 0.074 0.062
    #1 0.0730 0.0730 0.0695 0.118 0.112 0.073 0.070 0.005 1/16 0.062 0.0635 0.0625 0.031 0.025 0.007 0.087 0.075
    #2 0.0860 0.0860 0.0822 0.140 0.134 0.086 0.083 0.008 5/64 0.078 0.0791 0.0781 0.038 0.029 0.007 0.102 0.090
    #3 0.0990 0.0990 0.0949 0.161 0.154 0.099 0.095 0.008 5/64 0.078 0.0791 0.0781 0.044 0.034 0.007 0.115 0.102
    #4 0.1120 0.1120 0.1075 0.183 0.176 0.112 0.108 0.009 3/32 0.094 0.0952 0.0937 0.051 0.038 0.008 0.130 0.117
    #5 0.1250 0.1250 0.1202 0.205 0.198 0.125 0.121 0.012 3/32 0.094 0.0952 0.0937 0.057 0.043 0.008 0.145 0.132
    #6 0.1380 0.1380 0.1329 0.226 0.216 0.138 0.134 0.013 7/64 0.109 0.1111 0.1094 0.064 0.047 0.008 0.158 0.144
    #8 0.1640 0.1640 0.1585 0.270 0.257 0.164 0.159 0.014 9/64 0.141 0.1426 0.1406 0.077 0.056 0.008 0.188 0.172
    #10 0.1900 0.1900 0.1840 0.312 0.298 0.190 0.185 0.018 5/32 0.156 0.1587 0.1562 0.090 0.065 0.008 0.218 0.202
    #12 0.2160 0.2160 0.2095 0.324 0.314 0.216 0.210 0.022 5/32 0.156 0.1587 0.1562 0.103 0.082 0.010 - -
    1/4 0.2500 0.2500 0.2435 0.375 0.354 0.250 0.244 0.025 3/16 0.188 0.1900 0.1875 0.120 0.095 0.010 0.278 0.261
    5/16 0.3125 0.3125 0.3053 0.469 0.446 0.312 0.306 0.033 1/4 0.250 0.2530 0.2500 0.151 0.119 0.010 0.347 0.329
    3/8 0.3750 0.3750 0.3678 0.562 0.540 0.375 0.368 0.040 5/16 0.312 0.3160 0.3125 0.182 0.143 0.010 0.415 0.397
    7/16 0.4375 0.4375 0.4294 0.656 0.631 0.438 0.430 0.047 3/8 0.375 0.3790 0.3750 0.213 0.166 0.015 0.484 0.465
    1/2 0.5000 0.5000 0.4919 0.750 0.725 0.500 0.492 0.055 3/8 0.375 0.3790 0.3750 0.245 0.190 0.015 0.552 0.531
    9/16 0.5625 0.5625 0.5538 0.843 0.827 0.562 0.554 0.062 7/16 0.437 0.4420 0.4375 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 0.5050 0.5000 0.307 0.238 0.015 0.689 0.664
    3/4 0.7500 0.7500 0.7406 1.125 1.094 0.750 0.740 0.085 5/8 0.625 0.6310 0.6250 0.370 0.285 0.015 0.828 0.800
    7/8 0.8750 0.8750 0.8647 1.312 1.291 0.875 0.864 0.100 3/4 0.750 0.7570 0.7500 0.432 0.333 0.020 0.963 0.932
    1 1.0000 1.0000 0.9886 1.500 1.476 1.000 0.988 0.114 3/4 0.750 0.7570 0.7500 0.495 0.380 0.020 1.100 1.068
    1 1/8 1.1250 1.1250 1.1086 1.688 1.665 1.125 1.111 0.129 7/8 0.875 0.8850 0.8750 0.557 0.428 0.020 1.235 1.198
    1 1/4 1.2500 1.2500 1.2336 1.875 1.852 1.250 1.236 0.144 7/8 0.875 0.8850 0.8750 0.620 0.475 0.020 1.370 1.333
    1 3/8 1.3750 1.3750 1.3568 2.062 2.038 1.375 1.360 0.160 1 1.000 1.0200 1.0000 0.682 0.523 0.020 1.505 1.466
    1 1/2 1.5000 1.5000 1.4818 2.250 2.224 1.500 1.485 0.176 1 1.000 1.0200 1.0000 0.745 0.570 0.020 1.640 1.601
    1 3/4 1.7500 1.7500 1.7295 2.625 2.597 1.750 1.734 0.207 1 1/4 1.250 1.2750 1.2500 0.870 0.665 0.020 1.910 1.869
    2 2.0000 2.0000 1.9780 3.000 2.970 2.000 1.983 0.238 1 1/2 1.500 1.5300 1.5000 0.995 0.760 0.020 2.180 2.128
    2 1/4 2.2500 2.2500 2.2280 3.375 3.344 2.250 2.232 0.269 1 3/4 1.750 1.7850 1.7500 1.120 0.855 0.036 2.450 2.398
    2 1/2 2.5000 2.5000 2.4762 3.750 3.717 2.500 2.481 0.300 1 3/4 1.750 1.7850 1.7500 1.245 0.950 0.036 2.720 2.662
    2 3/4 2.7500 2.7500 2.7262 4.125 4.090 2.750 2.730 0.332 2 2.000 2.0400 2.0000 1.370 1.045 0.036 2.990 2.936
    3 3.0000 3.0000 2.9762 4.500 4.464 3.000 2.979 0.362 2 1/4 2.250 2.2950 2.2500 1.495 1.140 0.036 3.260 3.206
    3 1/4 3.2500 3.2500 3.2262 4.875 4.837 3.250 3.228 0.394 2 1/4 2.250 2.2950 2.2500 1.620 1.235 0.036 3.530 3.476
    3 1/2 3.5000 3.5000 3.4762 5.250 5.211 3.500 3.478 0.426 2 3/4 2.750 2.8050 2.7500 1.745 1.330 0.036 3.800 3.746
    3 3/4 3.7500 3.7500 3.7262 5.625 5.584 3.750 3.727 0.458 2 3/4 2.750 2.8050 2.7500 1.870 1.425 0.036 4.070 4.016
    4 4.0000 4.0000 3.9762 6.000 5.958 4.000 3.976 0.489 3 3.000 3.0600 3.0000 1.995 1.520 0.036 4.340 4.286

    ASME B18.3 Hexagon Socket Head Cap Screw Length Tolerances(Inch)

    Nominal Length Nominal Size, Tolerances on Lengths
    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
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