GB/T 1231-2024 High-Strength Large Hexagon Bolting Assemblies

This is the GB/T 1231 high-strength large hexagon bolting assembly product page. GB/T 1231-2024 is the Chinese standard for the hexagon-head bolting assembly used in structural steelwork — an assembly, not a single piece: one large hexagon-head bolt, one large hexagon nut, one washer A (under the bolt head) and one washer B (under the nut), matched from the same batch, supplied and tested as a set.

Relationship to the earlier editions: GB/T 1231-2024 (issued 2024-09-29, effective 2025-04-01) replaces GB/T 1231-2006, GB/T 1228-2006 (bolts), GB/T 1229-2006 (nuts) and GB/T 1230-2006 (washers), merging the latter three into the former. Compared with the previous edition the revision replaces the standard-deviation requirement on the torque coefficient with a coefficient-of-variation requirement, and adds sizes M33 and M36. Our GB/T 1231-2024 heavy hex structural bolt page (formerly the GB/T 1228-2006 page; single piece, quoted per piece) is still online for single-piece demand.

Why the set matters: the torque coefficient is a property of the assembly, not of the bolt alone. Clause 6.3.1 of GB/T 1231-2024 requires assemblies to be supplied with a guaranteed torque coefficient — batch mean K = 0.110–0.150 with a coefficient of variation VK ≤ 0.077 — and the coefficient is guaranteed for 6 months from the date of despatch. It is verified on 8 assemblies drawn per batch, and one batch covers at most 3,000 assemblies. Mixing bolts and nuts from different batches or suppliers scatters K and makes preload uncontrollable, so order by set and by batch.

Sizes made to order cover M12–M36 (M12, M16, M20, M22, M24, M27, M30, M33, M36 — nine diameters, 170 listed SKUs), lengths about 35–360 mm; the bolt is property class 10.9S, alloy steel, black oxide, supplied per set. Sizes below M12 are not covered, and unlisted diameters and lengths are quoted to your drawing. For the final tightening torque under the torque-control method, see the structural high-strength assembly mode of our torque calculator (M12–M36 preload taken from Table 14 of GB/T 1231-2024).

International standard relationships are entry points for buyers only: EN 14399 is the European series for high-strength structural bolting assemblies for preloading (parts such as -3 HR hexagon bolt and nut assemblies, and -10 HRC calibrated-preload assemblies), and large hexagon bolts are commonly referenced to ISO 7412 in the international system. Our alias registry does not register GB/T 1231 as equivalent to any of them, and we claim no third-party certification. On an inquiry quoting those standard numbers we supply complete sets to GB/T 1231 and confirm dimensions and classes item by item against your drawing. For torsion-shear assemblies — where the spline end is twisted off at the tightening axial force — see GB/T 3632 torsion-shear high-strength bolting assemblies. For non-preloaded connections see EN 15048 non-preloaded structural bolting assemblies.