Standards
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Bi-Hex / Double-Hex Bolts
Bi-hex bolts (also called double-hex bolts and 12-point bolts) are external-drive fasteners with twelve splines arranged every 30 degrees around the head. The geometry is widely used in aerospace structural fastening and motorsport engine internals because it delivers about 2x the wrench engagement angles of a standard hex head, allowing higher applied torque without camming the wrench off the joint, and a slightly lower head profile that is also very popular in tight engine bays where socket clearance is limited. The three names are interchangeable; UK and Australian engineering drawings tend to use "bi-hex", US drawings tend to use "12-point", and German drawings use "Vielzahn" or "double-hex".
TorqBolt manufactures bi-hex bolts in A286 (160 ksi aerospace), Inconel 718 (180 ksi turbine), Ti-6Al-4V (lightweight), MP35N (sour-service), AISI 8740 chromoly heat-treated (220 ksi race), Custom 465, AISI 4340, 17-4 PH, H-11 tool steel and L19 race-grade alloy steel under AS9100D Rev D and ISO 9001:2015 quality systems. Each bolt 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).
Materials
Alloy choice is set by the spec, the service temperature, the corrosion environment, and the strength target. TorqBolt routinely produces bi-hex bolts (also called double-hex bolts and 12-point bolts) 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.
Why 12 splines outperform 6-point hex
A standard hex (6-point) head allows the wrench to engage at every 60-degree rotation. A 12-point head doubles that, allowing engagement every 30 degrees. In a tight engine bay or aircraft assembly bay where the wrench cannot swing a full 60 degrees between obstacles, the 12-point geometry is the difference between being able to torque the bolt and not. The same alloy in a hex head and a 12-point head reaches the same tensile failure load (set by the bolt body, not the head); the 12-point lets you reach the design preload without cam-off, and the hex sometimes does not.
In aerospace use, the 12-point head appears across the MS21250, NAS1351, AS3216, and NAS6300-series specifications. In motorsport and diesel use, the 12-point appears on aftermarket head studs, connecting rod bolts, and main cap bolts. The internal-hexalobular drive (cap-screw recessed socket per ISO 14579) is a different system and is driven by a Torx-style internal driver, not the 12-point socket. The disambiguation is documented on the External vs Internal 12-Point page.
"Bi-hex" and "double-hex" are regional synonyms
The terms "bi-hex bolts" and "double-hex bolts" are used interchangeably with "12-point bolts" in different regions and industries. "Bi-hex" is more common in European mechanical engineering catalogs, "double-hex" appears in some American military procurement documents, and "12-point" is the standard term in US aerospace and motorsport. All three describe the same external head geometry: 12 splines arranged at 30-degree intervals around the bolt head perimeter, doubling the wrench engagement angles versus a 6-point hex.
Drawing callouts that say "bi-hex" or "double-hex" can be supplied as standard 12-point bolts under MS21250, NAS1351, AS3216, or NAS6303 through NAS6320 spec depending on tensile target and head dimension. The European DIN family (covered on DIN 12-point bolts) and the metric variants on metric 12-point use the same 12-spline head geometry. Confirm the tensile class (10.9 / 12.9 alloy steel, A286 stainless, or specialty alloy) and the head dimensions in the RFQ.
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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