ISO 4014 Hexagon Head Bolts with Partial Thread | M5 to M56, Property Class 8.8

Product Introduction
Metric hexagon head bolts manufactured to ISO 4014:2022 (superseding DIN 931). The bolt features a partial thread with an unthreaded shank section beneath the head. Thread sizes M5 to M56 in ISO metric coarse pitch with thread tolerance class 6g. The partial thread design positions the full-diameter shank across shear planes, preventing thread bearing from reducing joint integrity in shear-loaded connections. Widely used in structural steelwork, machinery assemblies, and bolted joints requiring high shear resistance.

Material & Mechanical Properties
Medium carbon steel, quenched and tempered to property class 8.8 per ISO 898-1. Minimum tensile strength: 800 MPa for M5–M16, 830 MPa for M17–M56. Minimum yield strength: 640 MPa for M5–M16, 660 MPa for M17–M56. Minimum elongation: 12% for diameters up to M16 and larger sizes. Hardness: 22–32 HRC for M5–M16, 23–34 HRC for larger sizes. Stainless steel variants conform to A2-70 (304, 700 MPa) and A4-80 (316, 800 MPa) per ISO 3506-1.

Geometry & Thread
Product grade A applies to threads up to M24 with nominal lengths ≤ 10d or 150 mm (whichever is shorter); grade B applies to larger threads or longer lengths. Key across-flats dimensions: M5 = 8.0 mm, M6 = 10.0 mm, M8 = 13.0 mm, M10 = 16.0 mm, M12 = 18.0 mm, M16 = 24.0 mm, M20 = 30.0 mm, M24 = 36.0 mm, M30 = 46.0 mm, M36 = 55.0 mm, M56 = 85.0 mm. Head height ranges from 3.5 mm (M5) to 35.0 mm (M56). Thread length (b) follows ISO 4014 tables; for example, M16 × 80 has b = 38 mm with a 42 mm unthreaded shank. ISO 4014 differs from DIN 931 in width across flats for M10, M12, M14, and M22.

Surface Finish
Standard finishes include zinc plating (clear, blue, or yellow passivation), hot-dip galvanizing (HDG), black oxide, Dacromet, and Geomet. For hot-dip galvanized bolts, threads are manufactured to tolerance class 6az (undersize) before coating per ISO 10684, ensuring final fit with standard 6H nuts after galvanizing.

Marking & Certification
Each bolt head is permanently marked with the property class (8.8) and the manufacturer’s identification mark. Stainless steel bolts additionally carry the material grade (A2 or A4) and strength class (–70 or –80). Full traceability is maintained from mill certificate to shipment. EN 10204 Type 3.1 inspection certificates are available, providing chemical analysis, mechanical properties, and heat identification. Dimensional inspection includes 100% check of across flats, head height, thread length, and radius under head; Go/No-Go thread gauging is performed on every batch.

Application Suitability
Structural steelwork, machinery frames, pressure vessels, and general engineering joints where a partial-thread hexagon bolt with high shear capacity is required. The unthreaded shank allows the shear plane to intersect the full-diameter section, improving load-carrying capacity compared to fully threaded fasteners. Suitable for both static and dynamic loading when installed to the relevant design code.