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    12-Point Cap Screws

    12-Point Cap Screws, TorqBolt 12-point fastener with tB ligature and alloy grade marking

    12-point cap screws are externally driven tension fasteners with a fully threaded or close-tolerance shank and a 12-spline external head, very popular in aerospace structural joints and high-RPM engine internals because the twelve splines deliver about 2x the wrench engagement angles of a standard hex head and let the fastener be tightened to a higher preload before the wrench cams off the joint. The 12-point cap-screw family covers NAS6303 through NAS6320 aerospace tension cap screws (1/4" through 1-1/4" body) and customer-spec engine builders' cap screws.

    TorqBolt manufactures 12-point cap screws in A286 (160 ksi for aerospace), AISI 8740 chromoly heat-treated (up to 220 ksi for race engines), Inconel 718 (180 ksi superalloy), 17-4 PH and Custom 465 to AS9100D Rev D and ISO 9001:2015 quality systems. Each cap-screw head carries the struck tB manufacturer ligature plus the alloy grade marking, and every lot ships with a mill test report (MTC 3.1 standard, MTC 3.2 critical with third-party witness inspection of chemistry, hardness, tensile and dimensional records).

    Materials

    Alloy choice is set by the spec, the service temperature, the corrosion environment, and the strength target. TorqBolt routinely produces 12-point cap screws in A286 (UNS S66286), Inconel 718, Ti-6Al-4V (Grade 5), MP35N (UNS R30035), Custom 465 stainless, AISI 8740 chromoly heat-treated, AISI 4340, 17-4 PH H1025 condition, H-11 tool steel, and L19 race-grade alloy steel.

    UNJ-3A External Thread Dimensions (Common 12-Point Bolt Sizes)

    Per SAE AS8879 (controlled-root-radius UNJ external thread). 12-point aerospace bolts under MS21250, NAS1351, AS3216, NAS6303 to NAS6320 are produced to UNJ-3A external thread tolerances. Root radius 0.150 P to 0.180 P (where P = pitch) for fatigue resistance, this is the difference vs standard UN-3A and the reason aerospace specifies UNJ.

    NominalTPIPitch P (mm)Major Dia Min (mm)Major Dia Max (mm)Pitch Dia Min (mm)Pitch Dia Max (mm)Minor Dia Min (mm)Minor Dia Max (mm)
    1/4-28 UNJF-3A280.9076.2976.3505.7065.7705.1565.296
    5/16-24 UNJF-3A241.0587.8757.9387.1857.2496.5536.711
    3/8-24 UNJF-3A241.0589.4629.5258.7738.8408.1398.298
    7/16-20 UNJF-3A201.27011.05111.11310.22710.2979.4679.652
    1/2-20 UNJF-3A201.27012.63812.70011.81511.88711.05111.243
    9/16-18 UNJF-3A181.41114.22514.28813.31013.38512.46612.673
    5/8-18 UNJF-3A181.41115.81215.87514.89714.97314.05414.262
    3/4-16 UNJF-3A161.58818.99119.05017.96118.04017.01817.246
    7/8-14 UNJF-3A141.81422.16622.22521.00121.08519.92620.181
    1-12 UNJF-3A122.11725.33625.40023.97424.06422.71722.985
    1 1/4-12 UNJF-3A122.11731.68731.75030.32830.41829.07229.343
    1 1/2-12 UNJF-3A122.11738.03738.10036.67836.76835.42235.693
    1 15/16-12 UNJF-3A122.11749.14949.21347.79147.88646.53546.812
    2-12 UNJF-3A122.11750.73750.80049.37849.47348.12248.399

    Internal thread (UNJ-3B, mating nut) tolerances and metric M-J equivalents available on request. Send drawing or spec callout to info@torqbolt.com.

    Request a Quote

    RFQ to info@torqbolt.com, call +91-22-66157017, or WhatsApp +91-22-66157017. Mill test report (MTC 3.1 standard, 3.2 critical-service) ships with every lot.

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