Class 8.8 Hex Purlin Bolt Assemblies: Dimensions and Tightening Torque Data Sheet

Key things to remember

The essentials from this document in plain words. Check the full document before you rely on a figure.

• ✓Each assembly is a class 8.8 bolt, a class 8 nut and two washers, zinc plated (ZP) or hot dip galvanised (HDG).
• ✓Sizes: M12 x 30 (HDG or ZP) and M16 x 30, M16 x 40, M16 x 45 (ZP), part numbers KBHHTGCM120030 to KBHHTZCM160045.
• ✓Indicative tightening torque: M12 73.0Nm galvanised, 64.0Nm zinc plated; M16 zinc plated 160.0Nm. Use it only when the engineer or purlin supplier gives no torque.
• ✓The torque is worked out for a bolt tension of 50% of proof load (24,450N for M12, 45,500N for M16), with a friction factor of 0.22 for zinc plated and 0.25 for galvanised. Thread condition, lubrication and site conditions change this, so the engineer should set the final figure.
• ✓Dimensions: M12 head and nut 18mm across flats, washers 32mm outside, 14mm inside, 2.0mm thick; M16 24mm across flats, washers 34mm, 18mm and 2.5mm.
• ✓Keep the assembly square: the head and nut must bear fully on the washers and the washers on the parts being fastened. Hole sizes to AS 4600 or as the designing engineer specifies.

Who it helps: Builders and engineers fixing purlins with high tensile bolts, and staff checking sizes and torque.