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    External vs Internal 12-Point Drive Systems

    External vs Internal 12-Point Drive Systems, TorqBolt 12-point fastener with tB ligature and alloy grade marking

    Two different bolt drive systems get confused because both involve twelve features on the bolt head. They are on different sides of the head and require different drivers.

    PropertyExternal 12-pointInternal hexalobular (ISO 14579)
    Drive locationOutside of head (12 splines)Inside of head (6-lobe star socket)
    Driver tool12-point socket wrenchHexalobular / Torx internal driver
    Common specMS21250, NAS1351, AS3216ISO 14579
    Primary marketUS aerospace + motorsportEuropean industrial cap screws
    Head styleBolt head with external splinesCap screw with recessed socket

    How to tell which drive system your drawing calls out

    For the full ISO 14579 disambiguation page see ISO 14579 (Internal). For the 12-point socket tool clarification see 12-Point Socket (Tool).

    Need Either?

    TorqBolt manufactures both. Specify drive type (external 12-point or internal hexalobular ISO 14579) clearly in your RFQ. Email info@torqbolt.com.

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    Frequently asked questions

    What is a 12-point bolt?

    A 12-point bolt has 12 splines arranged every 30 degrees on the OUTSIDE of the bolt head, also called a bi-hex or double-hex bolt. The 12 external splines provide twice the wrench-engagement angles of a standard hex head, allowing higher applied torque before cam-off, which is why aerospace and motorsport applications adopt the geometry.

    Are 12-point bolts the same as ISO 14579?

    No. ISO 14579 specifies an INTERNAL hexalobular socket head (similar to Torx) recessed inside a cap screw. External 12-point bolts under MS21250 / NAS1351 / AS3216 use an EXTERNAL bi-hex head driven by a 12-point socket wrench. Both involve 12 features but on different sides of the bolt head and require different drivers.

    Which alloys does TorqBolt manufacture 12-point bolts in?

    TorqBolt produces 12-point bolts in A286 (UNS S66286), Inconel 718 (UNS N07718), Ti-6Al-4V Grade 5, MP35N (UNS R30035), Custom 465 H1025, AISI 8740 chromoly heat-treated, AISI 4340, 17-4 PH, H-11 tool steel, and L19 race-grade alloy steel. Choice depends on tensile target, service temperature, and corrosion environment.

    Is TorqBolt AS9100D certified?

    Yes. TorqBolt operates under AS9100D Rev D and ISO 9001:2015 quality management systems, audited annually by the registrar. NORSOK M-630 and NACE MR0175 / ISO 15156 qualifications cover offshore and sour-service applications. Mill test reports MTC 3.1 standard and MTC 3.2 critical-service witness are issued with every lot.

    What lead time should I expect?

    Stock alloys (A286, AISI 8740, AISI 4340, 17-4 PH, 316 stainless) ship in 4 to 6 weeks. Specialty alloys (Inconel 718, MP35N, Custom 465, Ti-6Al-4V, L19) ship in 8 to 12 weeks depending on raw-bar lead time at the alloy producer. Critical-service orders requiring third-party witness inspection (MTC 3.2) add 1 to 2 weeks for witness scheduling.