AS/NZS 1252 High-Strength Structural Bolt Assemblies | Class 8.8, Hot-Dip Galvanized

Product Introduction
Complete high-strength structural bolting assemblies manufactured and verified to AS/NZS 1252.1:2016 (Technical Requirements) and AS/NZS 1252.2:2016 (Verification Testing). Each assembly comprises a property class 8.8 hexagon head bolt, a property class 8 hexagon nut, and a hardened and tempered washer. Diameters M16 to M36 with ISO metric coarse pitch. Hot-dip galvanized finish to AS/NZS 4680 for external and exposed environments. The 2016 revision introduced K-class classification (K0, K1, K2) based on assembly verification testing to determine the nut factor (k-value) for torque-controlled installation.

Material & Mechanical Properties
Bolt: property class 8.8 per AS 4291.1, minimum tensile strength 830 MPa, minimum yield strength 660 MPa. Nut: property class 8, proof load stress matched to bolt tensile capacity. Washer: hardened and tempered to 320–390 HV (33–41 HRC) for both plain and hot-dip galvanized condition. Mechanical properties are certified by lot with heat-number traceability.

Geometry & Thread
Thread sizes and coarse pitches: M16 (2.00 mm), M20 (2.50 mm), M24 (3.00 mm), M30 (3.50 mm), M36 (4.00 mm). Head across-flats: M16 = 26.16–27.00 mm; M20 = 31.00–32.00 mm; M24 = 40.00–41.00 mm. Head height ranges from 9.25–10.75 mm (M16) to 21.45–23.55 mm (M36). Washer for M16: inside diameter 15.3–16.7 mm, outside diameter 38–44 mm. Thread tolerance is 6g applied before hot-dip galvanizing to ensure proper fit after coating.

Hot-Dip Galvanized Coating
Coating to AS/NZS 4680 provides a minimum average thickness of 50 μm on threads per AS/NZS 1214. For non-threaded surfaces, minimum average thickness is 45 μm for steel up to 1.5 mm, 55 μm for 1.5–3 mm, and 70 μm for 3–6 mm. Under AS/NZS 1252.1, nuts are galvanized as blanks and the threads are cut after galvanizing to maintain proper thread fit.

K-Class Verification
Assemblies are classified as K0, K1, or K2 based on the bolt assembly test per Appendix D of AS/NZS 1252.1. K0 assemblies have not undergone extended assembly testing and cannot be used for torque-controlled tensioning. K1 and K2 assemblies have a calibrated torque-tension relationship and may be used for torque-controlled installation. The K-class establishes the nut factor (km) used in the formula Mk = km × d × Fp,c to calculate the torque required for minimum bolt preload.

Marking & Certification
Bolt head permanently marked with property class “8.8”, manufacturer’s identification mark, and batch traceability code. Assemblies are supplied as matched sets from a single manufacturer. Verification testing is performed by an independent accredited laboratory to AS/NZS 1252.2. Certification documentation is available with each batch.

Application Suitability
Steel-to-steel structural connections in buildings, bridges, and infrastructure projects executed to Australian and New Zealand standards. The hot-dip galvanized finish provides sacrificial corrosion protection for external, coastal, and industrial environments. K1 and K2 assemblies are suitable for torque-controlled preloading where the calibrated nut factor is applied to determine installation torque.