Buy Purlin Bolts Nuts Online in Australia
Purlin Bolt & Nut Quick Reference
Purlin bolts are hex flange fasteners connecting roof purlins, wall girts and secondary structural framing to primary steel frames. The flange head + flange nut distribute load over thin-section purlin, preventing pull-through (the failure mode for standard bolts in light-gauge sections). AIMS stocks Bremick and Hobson purlin bolts in multiple grades and finishes.
| Bolt Size | Common Lengths | Grade Standard | Best For |
|---|---|---|---|
| M10 | 20, 25, 30, 35, 40, 50 mm | Grade 4.6 ZP / Grade 8.8 HDG | Light-duty secondary connections — small purlins, lightweight cladding rails |
| M12 | 25, 30, 35, 40, 50, 65, 80 mm | Grade 4.6 ZP / Grade 8.8 HDG | Workshop default for standard purlin work |
| M16 | 30, 40, 50, 65, 80, 100 mm | Grade 4.6 ZP / Grade 8.8 HDG | Heavier purlins, structural connections, larger building frames |
| M20 | 50, 65, 80, 100 mm | Grade 8.8 HDG | Heavy industrial buildings, large mass framing |
Grade selection: 4.6 ZP for non-critical secondary connections. 8.8 HDG for outdoor + structural applications (galvanised for corrosion resistance). For matching nuts: hex flange nuts of same size + grade + finish. For Tek screws as an alternative on light-gauge purlins, see self-tapping screws with our guide. Companion: structural bolts, coach bolts, dynabolts.
Purlin Bolts & Nuts — Structural Fasteners for Steel Framing and Roof Purlins
Purlin bolts are specially designed hex flange fasteners used to connect roof purlins, wall girts and secondary structural steel framing to primary steel frames. The flange head and nut distribute load over the thin-section purlin, preventing pull-through — a failure mode that can occur with standard bolts in light-gauge sections. AIMS Industrial stocks purlin bolts and nuts from Bremick and Hobson in multiple grades and finishes.
Grades and Finishes
Grade 4.6 purlin bolts are the standard specification for secondary structural connections in non-critical steel framing. Zinc plated (ZP) Grade 4.6 is used in protected internal applications; hot-dip galvanised (HDG) Grade 4.6 is specified for external and coastal applications where corrosion resistance is required.
Grade 8.8 purlin bolts are high-tensile, providing greater clamping force for structural connections subject to higher loads — including wind uplift connections and primary frame connections in engineered steel buildings. Available in both zinc plated and hot-dip galvanised finishes.
Types
Hex flange bolt and nut kits include the purlin bolt and matching flange nut as a matched pair — reducing the risk of grade mismatch between bolt and nut. M12 bulk packs (200 piece and 150 piece) are available for volume installation work.
Shoulder purlin bolts have a stepped shoulder below the flange head — providing a bearing surface for shear load transfer at beam and column connections.
Standards and Specification
Purlin bolts should be specified in accordance with AS 4600 (Cold-Formed Steel Structures) and the building manufacturer's specification. The bolt grade, diameter, length and finish must match the engineer's design requirement. Do not substitute a lower grade or lighter finish than specified.
Need purlin bolts in bulk quantities or non-standard specifications? Contact our team.
People Also Ask — Purlin Bolts and Nuts
Q: What's a purlin bolt?
A purlin bolt is a specialised high-tensile bolt with a square neck under the head — used to attach steel purlins (the horizontal members supporting roof and wall cladding) to rafters or columns. The square neck locks into a punched square hole in the cladding bracket, preventing the bolt from rotating during nut tightening. Common in Australian commercial and industrial steel construction — typically Grade 8.8 zinc-plated, with hex nuts and washers in matching sets.
Q: What sizes are purlin bolts available in?
Common workshop and construction sizes: M12 × 25mm, M12 × 30mm, M12 × 35mm, M12 × 40mm, plus M16 sizes for heavier purlin connections. The bolt length must match the cladding bracket thickness plus nut engagement. Australian commercial steel buildings predominantly use M12 purlin bolts — refer to the building's structural drawings for the specific length required.
Q: Galvanised or zinc-plated purlin bolts?
Standard zinc-plated (electroplated zinc) for indoor-clad and conditioned environments. Hot-dip galvanised (HDG) for outdoor and coastal exposure — much thicker zinc layer, longer corrosion life. Stainless 316 for severe coastal or chemical exposure environments. Match the bolt finish to the building's environment. Don't use plain steel purlin bolts in any building — they rust fast and weaken the structural connection.
Q: What torque for M12 purlin bolts?
Grade 8.8 M12: approximately 80-90 Nm for snug-tight in dry threads, higher (110-130 Nm) for full-tension installation per AS 4100 structural steel specs. Follow the structural engineer's specification on critical connections — the design may call for snug-tight, snug-plus-turn, or full preload. Don't over-torque purlin bolts without engineer approval; over-tensioning can damage the bolt or strip the threads.
Q: Do I need washers on purlin bolts?
Yes for most installations — a flat washer under the nut spreads load on the bracket face. Sometimes also a flat washer under the bolt head (depends on the bracket design). Spring washers are not commonly used on purlin bolts because the snug-tight nut clamping force handles vibration resistance in a structural connection. Always include washers unless the structural drawing specifically omits them.