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    2. B18.3 Spline Socket Head Cap Screws

    ASME B18.3 Spline Socket Head Cap Screws – Dimensions, Specifications & Standards

    Spline Socket Head Cap Screws for High-Torque & Tamper-Resistant Fastening.

    ASME B18.3 Spline Socket Head Cap Screws are inch-series precision fasteners with a multi-spline internal drive socket in a cylindrical head, transmitting significantly higher torque than standard hexagon socket designs while offering enhanced tamper resistance in security-sensitive or high-vibration environments. B18.3 defines head diameter, head height, spline socket dimensions, body diameter, thread length, and key engagement depth. These screws are manufactured under ASTM A1014/A1014M for UNS N07718 (Inconel 718) bolting, providing superior corrosion resistance, high-temperature strength, and anti-galling properties for oil and gas, aerospace, and petrochemical environments. Alloy steel versions per ASTM A574 offer 180,000 PSI minimum tensile strength. The multi-spline drive reduces tool cam-out, making these screws preferred for automated assembly and power-tool operations.

    Spline Socket HEAD CAP SCREW INCH THREAD

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

    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    		 Total
    Thread Length,
    L TT
    Max. Min. Max. Min. Max. Min. Max. Min. Min. Max. Min. Max.
    0 (0.0600) 1.52 1.45 2.44 2.31 1.52 1.45 0.10 1.52 0.64 0.51 0.18 12.70 15.75
    1 (0.0730) 1.85 1.78 3.00 2.84 1.85 1.78 0.13 1.83 0.79 0.64 0.18 15.75 19.56
    2 (0.0860) 2.18 2.08 3.56 3.40 2.18 2.11 0.20 2.44 0.97 0.74 0.18 15.75 20.32
    3 (0.0990) 2.51 2.41 4.09 3.91 2.51 2.41 0.20 2.44 1.12 0.86 0.18 15.75 21.08
    4 (0.1120) 2.84 2.74 4.65 4.47 2.84 2.74 0.23 2.82 1.30 0.97 0.20 19.05 25.15
    5 (0.1250) 3.18 3.05 5.21 5.03 3.18 3.07 0.30 2.82 1.45 1.09 0.20 19.05 25.40
    6 (0.1380) 3.51 3.38 5.74 5.54 3.51 3.40 0.33 3.38 1.63 1.19 0.20 19.05 26.67
    8 (0.1640) 4.17 4.04 6.86 6.65 4.17 4.04 0.36 4.27 1.96 1.42 0.20 22.35 30.23
    10 (0.1900) 4.83 4.67 7.92 7.70 4.83 4.70 0.46 4.65 2.29 1.65 0.20 22.35 32.26
    1/4 (0.2500) 6.35 6.20 9.53 9.27 6.35 6.20 0.64 5.49 3.05 2.41 0.25 25.40 38.10
    5/16 (0.3125) 7.95 7.75 11.91 11.61 7.92 7.77 0.84 7.39 3.84 3.02 0.25 28.45 43.43
    3/8 (0.3750) 9.53 9.35 14.27 13.97 9.53 9.35 1.02 9.45 4.62 3.63 0.25 31.75 49.28
    7/16 (0.4375) 11.13 10.90 16.66 16.31 11.13 10.92 1.19 11.53 5.41 4.22 0.38 35.05 55.12
    1/2 (0.5000) 12.70 12.50 19.05 18.67 12.70 12.50 1.40 11.53 6.22 4.83 0.38 38.10 60.45
    5/8 (0.6250) 15.88 15.65 23.83 23.39 15.88 15.65 1.78 15.11 7.80 6.05 0.38 44.45 71.63
    3/4 (0.7500) 19.05 18.82 28.58 28.12 19.05 18.80 2.16 15.75 9.40 7.24 0.38 50.80 82.55
    7/8 (0.8750) 22.23 21.97 33.32 32.84 22.23 21.95 2.54 17.73 10.97 8.46 0.51 57.15 93.73
    1 (1.0000) 25.40 25.12 38.10 37.57 25.40 25.10 2.90 20.07 12.57 9.65 0.51 63.50 104.65
    1 1/8 (1.1250) 28.58 28.17 42.88 42.29 28.58 28.22 3.28 ... 14.15 10.87 0.51 71.37 118.11
    1 1/4 (1.2500) 31.75 31.34 47.63 47.04 31.75 31.39 3.66 ... 15.75 12.07 0.51 79.25 129.29
    1 3/8 (1.3750) 34.93 34.47 52.37 51.77 34.93 34.54 4.06 ... 17.32 13.28 0.51 87.38 143.51
    1 1/2 (1.5000) 38.10 37.64 57.15 56.49 38.10 37.72 4.47 ... 18.92 14.48 0.51 95.25 154.43
    1 3/4 (1.7500) 44.45 43.94 66.68 65.96 44.45 44.04 5.26 ... 22.10 16.89 0.51 111.25 181.10
    2 (2.0000) 50.80 50.24 76.20 75.44 50.80 50.37 6.05 ... 25.27 19.30 0.51 127.00 206.00
    2 1/4 (2.2500) 57.15 56.59 85.73 84.94 57.15 56.69 6.83 ... 28.45 21.72 0.91 142.75 228.35
    2 1/2 (2.5000) 63.50 62.89 95.25 94.41 63.50 63.02 7.62 ... 31.62 24.13 0.91 158.75 254.00
    2 3/4 (2.7500) 69.85 69.24 104.78 103.89 69.85 69.34 8.43 ... 34.80 26.54 0.91 174.75 276.10
    3 (3.0000) 76.20 75.59 114.30 113.39 76.20 75.67 9.22 ... 37.97 28.96 0.91 190.50 298.45
    3 1/4 (3.2500) 82.55 81.94 123.83 122.86 82.55 81.99 10.01 ... 41.15 31.37 0.91 206.25 320.80
    3 1/2 (3.5000) 88.90 88.29 133.35 132.36 88.90 88.34 10.82 ... 44.32 33.78 0.91 222.25 342.90
    3 3/4 (3.7500) 95.25 94.64 142.88 141.83 95.25 94.67 11.63 ... 47.50 36.20 0.91 238.25 365.00
    4 (4.0000) 101.60 100.99 152.40 151.33 101.60 100.99 12.42 ... 50.67 38.61 0.91 254.00 387.35

    ASME B18.3 Spline Socket Head Cap Screw Length Tolerances(mm)

    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 25.4, incl. -0.762 -0.762 -1.270 ...
    Over 25.4 to 63.5, incl. -1.016 -1.524 -2.540 -4.572
    Over 63.5 to 152.4, incl. -1.524 -2.032 -3.556 -5.080
    Over 152.4 -3.048 -3.048 -5.080 -6.096
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