DIN 6914 HV Heavy Hex Structural Bolts | Class 10.9, Zinc Plated

Product Introduction
Heavy hex structural bolts manufactured to the dimensional and mechanical requirements of DIN 6914 / EN 14399-4, System HV (Hochfest Vorgespannt). DIN 6914 is the legacy German standard, now superseded by EN 14399-4. Property class 10.9. Diameters M12, M16, M20, M22, M24, M27, M30, and M36; lengths 30 mm to 250 mm. The large hexagon head is designed for high-torque preloading. System HV assemblies are used in friction-grip (slip-critical) connections where clamping force, not shank shear strength, carries the design load.

Material & Mechanical Properties
Property class 10.9 per ISO 898-1: minimum tensile strength 1040 MPa, minimum yield strength 940 MPa, stress under proof load 940 MPa, hardness 32–39 HRC. Quenched and tempered alloy steel, typically 42CrMo or equivalent. For hot-dip galvanized versions, threads are manufactured with oversize tolerance 6az before coating to maintain assembly fit after zinc application. System HV achieves ductility predominantly by plastic deformation of the engaged threads within a thinner nut (approximately 0.8d height), rather than by bolt elongation as in System HR.

Geometry & Thread
Thread pitches per ISO 261: M12 = 1.75 mm, M16 = 2.0 mm, M20 = 2.5 mm, M22 = 2.5 mm, M24 = 3.0 mm, M27 = 3.0 mm, M30 = 3.5 mm, M36 = 4.0 mm. Head height ranges from 8 mm (M12) to 23 mm (M36); width across flats from 22 mm (M12) to 60 mm (M36). Width across flats for common sizes: M20 = 32 mm, M24 = 41 mm, M36 = 60 mm. Thread length for standard lengths ranges from 23 mm (M12) to 52 mm (M36). Partial thread (shank) design.

Surface Finish
Zinc plated finish, either electroplated or hot-dip galvanized, provides corrosion protection for outdoor and industrial environments. The matching nut to EN 14399-4 (DIN 6915) is property class 10 with proof load stress 1160 MPa and a black molybdenum disulphide lubricant applied for consistent K-factor during preloading. Two washers to EN 14399-6 (DIN 6916), hardness 300–370 HV, are required: one under the head, one under the nut.

Marking & Certification
Bolt head marked with “HV” (system identifier), property class 10.9, manufacturer identification, and a production lot number for traceability. CE marking under the Construction Products Regulation references hEN 14399-4. A 3.1 inspection certificate is not automatically required because the lot number stamped on the head provides full traceability; it can be requested separately.

System Compatibility
Bolt, nut, and both washers must be supplied as a matched assembly from a single manufacturer. Components are not interchangeable between suppliers. Installation follows EN 1090-2 and EN 1993-1-8, with preloading achieved via the torque control method (K-class K1).

Application Suitability
Friction-grip (slip-critical) connections in steel structures where design load is carried by clamping force rather than shank shear. Used in bridges, heavy steel buildings, industrial plant, and infrastructure projects executed to Eurocode 3. The large head geometry accommodates the high torque required for preloading.