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    2. B18.3 Spline Socket Head Cap Screws

    ASME B18.3 Spline Socket Head Cap Screws Dimensions

    Spline socket head cap screws manufactured according to ASME B18.3 fastening specifications.

    ASME B18.3 Spline Socket Head Cap Screws are used in aerospace, automotive, heavy machinery, and high-torque industrial applications. These spline socket screws provide enhanced torque transfer, secure engagement, and reliable fastening performance for critical bolted assemblies.

    Spline Socket HEAD CAP SCREW INCH THREAD

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

    Nominal Size
    (Basic Screw Diameter)    		 Body Diameter, D Head Diameter, A Head Height, H Chamfer
    or Radius, C    		 Nominal
    Spline Socket
    Size, M    		 Key
    Engagement, T    		 Wall
    Thickness, G    		 Chamfer
    or Radius, K    		 Thread Length,
    L T (in)    		 Total
    Thread Length,
    L TT (in)
    Max. Min. Max. Min. Max. Min. Max. Min. Min. Max. Min. Max.
    0 (0.0600) 0.060 0.057 0.096 0.091 0.060 0.057 0.004 0.06 0.025 0.020 0.007 0.50 0.62
    1 (0.0730) 0.073 0.070 0.118 0.112 0.073 0.070 0.005 0.072 0.031 0.025 0.007 0.62 0.77
    2 (0.0860) 0.086 0.082 0.140 0.134 0.086 0.083 0.008 0.096 0.038 0.029 0.007 0.62 0.80
    3 (0.0990) 0.099 0.095 0.161 0.154 0.099 0.095 0.008 0.096 0.044 0.034 0.007 0.62 0.83
    4 (0.1120) 0.112 0.108 0.183 0.176 0.112 0.108 0.009 0.111 0.051 0.038 0.008 0.75 0.99
    5 (0.1250) 0.125 0.120 0.205 0.198 0.125 0.121 0.012 0.111 0.057 0.043 0.008 0.75 1.00
    6 (0.1380) 0.138 0.133 0.226 0.218 0.138 0.134 0.013 0.133 0.064 0.047 0.008 0.75 1.05
    8 (0.1640) 0.164 0.159 0.270 0.262 0.164 0.159 0.014 0.168 0.077 0.056 0.008 0.88 1.19
    10 (0.1900) 0.190 0.184 0.312 0.303 0.190 0.185 0.018 0.183 0.090 0.065 0.008 0.88 1.27
    1/4 (0.2500) 0.250 0.244 0.375 0.365 0.250 0.244 0.025 0.216 0.120 0.095 0.010 1.00 1.50
    5/16 (0.3125) 0.313 0.305 0.469 0.457 0.312 0.306 0.033 0.291 0.151 0.119 0.010 1.12 1.71
    3/8 (0.3750) 0.375 0.368 0.562 0.550 0.375 0.368 0.040 0.372 0.182 0.143 0.010 1.25 1.94
    7/16 (0.4375) 0.438 0.429 0.656 0.642 0.438 0.430 0.047 0.454 0.213 0.166 0.015 1.38 2.17
    1/2 (0.5000) 0.500 0.492 0.750 0.735 0.500 0.492 0.055 0.454 0.245 0.190 0.015 1.50 2.38
    5/8 (0.6250) 0.625 0.616 0.938 0.921 0.625 0.616 0.070 0.595 0.307 0.238 0.015 1.75 2.82
    3/4 (0.7500) 0.750 0.741 1.125 1.107 0.750 0.740 0.085 0.62 0.370 0.285 0.015 2.00 3.25
    7/8 (0.8750) 0.875 0.865 1.312 1.293 0.875 0.864 0.100 0.698 0.432 0.333 0.020 2.25 3.69
    1 (1.0000) 1.000 0.989 1.500 1.479 1.000 0.988 0.114 0.79 0.495 0.380 0.020 2.50 4.12
    1 1/8 (1.1250) 1.125 1.109 1.688 1.665 1.125 1.111 0.129 ... 0.557 0.428 0.020 2.81 4.65
    1 1/4 (1.2500) 1.250 1.234 1.875 1.852 1.250 1.236 0.144 ... 0.620 0.475 0.020 3.12 5.09
    1 3/8 (1.3750) 1.375 1.357 2.062 2.038 1.375 1.360 0.160 ... 0.682 0.523 0.020 3.44 5.65
    1 1/2 (1.5000) 1.500 1.482 2.250 2.224 1.500 1.485 0.176 ... 0.745 0.570 0.020 3.75 6.08
    1 3/4 (1.7500) 1.750 1.730 2.625 2.597 1.750 1.734 0.207 ... 0.870 0.665 0.020 4.38 7.13
    2 (2.0000) 2.000 1.978 3.000 2.970 2.000 1.983 0.238 ... 0.995 0.760 0.020 5.00 8.11
    2 1/4 (2.2500) 2.250 2.228 3.375 3.344 2.250 2.232 0.269 ... 1.120 0.855 0.036 5.62 8.99
    2 1/2 (2.5000) 2.500 2.476 3.750 3.717 2.500 2.481 0.300 ... 1.245 0.950 0.036 6.25 10.00
    2 3/4 (2.7500) 2.750 2.726 4.125 4.090 2.750 2.730 0.332 ... 1.370 1.045 0.036 6.88 10.87
    3 (3.0000) 3.000 2.976 4.500 4.464 3.000 3.979 0.363 ... 1.495 1.140 0.036 7.50 11.75
    3 1/4 (3.2500) 3.250 3.226 4.875 4.837 3.250 3.228 0.394 ... 1.620 1.235 0.036 8.12 12.63
    3 1/2 (3.5000) 3.500 3.476 5.250 5.211 3.500 3.478 0.426 ... 1.745 1.330 0.036 8.75 13.50
    3 3/4 (3.7500) 3.750 3.726 5.625 5.584 3.750 3.727 0.458 ... 1.870 1.425 0.036 9.38 14.37
    4 (4.0000) 4.000 3.976 6.000 5.958 4.000 3.976 0.489 ... 1.995 1.520 0.036 10.00 15.25

    ASME B18.3 Spline 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

    Frequently Asked Questions

    What grades of nonferrous metal does ASTM F468 cover for spline drive bolts?

    ASTM F468 covers copper (C11000), brass (C26000, C27000, C46200, C46400), bronze (C51000 phosphor, C61300/C61400/C63000 aluminum, C64200, C65100/C65500/C66100 silicon, C67500 manganese), cupro-nickel (C71000, C71500), nickel-base alloys (N04400 Monel 400, N04405, N05500 Monel K-500, N06059 Alloy 59, N06625 Inconel 625, N06686, N10001 Hastelloy B-2, N10276 Hastelloy C-276), aluminum (A92024, A96061, A97075), and titanium (R50250 Gr 1, R50400 Gr 2, R50700 Gr 4, R56400 Gr 5, R56401 Gr 23 ELI, R52400 Gr 7, R58640 Gr 19, R55111 Gr 32) - all available for this product family at TorqBolt.

    What is the dimensional standard for these spline drive bolts?

    This product follows ASME B18.3, the dimensional standard for spline drive bolts. Material chemistry, mechanical properties, and acceptance criteria follow ASTM F468 / F468M for nonferrous bolting. TorqBolt supplies both inch-series and metric sizes per the applicable ASME or ISO drawing.

    Which F468 grades are best for marine and seawater service?

    For seawater bolting per F468: Monel 400 (N04400) and Monel K-500 (N05500) resist chloride stress-corrosion cracking and HF acid; nickel-aluminum bronze C63000 is the standard high-strength marine fastener; cupro-nickel C71500 is preferred for condenser tube-sheet bolting; naval brass C46400 is the lower-cost option for routine marine hardware; titanium Grade 2 (R50400) is the premium choice for severe chloride + chemical service.

    Are F468 spline drive bolts NACE MR0175 acceptable for sour service?

    Most F468 nickel and titanium grades are NACE MR0175 / ISO 15156-listed: Monel 400 (N04400), Monel K-500 (N05500) conditional, Inconel 625 (N06625), Hastelloy B-2 (N10001), Hastelloy C-276 (N10276), Alloy 59 (N06059), Alloy 686 (N06686), and all titanium grades (R50400, R52400, R56400, R56401). Aluminum bronzes are generally not preferred for sour service. TorqBolt provides NACE-compliant heat-treat and hardness reports on request.

    References & Standards

    • ASTM F468 / F468M - Standard Specification for Nonferrous Bolts, Hex Cap Screws, and Studs for General Use
    • ASTM F467 / F467M - Companion specification for Nonferrous Nuts (mate with F468 for matched-alloy assemblies)
    • ASTM F436 / F436M - Hardened steel washers (ferrous washer companion when nonferrous washers are not specified)
    • NACE MR0175 / ISO 15156 - Sour-service hardness limits for petroleum and natural gas industries
    • ASME B18.2.1 / B18.2.3 series / B18.3 / B18.6.7M / B18.31 / B16.5 - Dimensional standards referenced by F468
    • DIN 912 / 933 / 931 - Metric hex socket head and hex head cap screw dimensional standards
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