Purlin Bolt

Purlin bolts: what is in each kit

Purlin bolts fix steel purlins and girts in sheds, garages, carports, warehouses and other steel-framed buildings. Hobson lists them for fixing purlins and other thin gauge metal components, roofing and framing in steel construction, industrial and commercial warehouses, and rural and residential sheds and garages. Every kit comes with its nut, so there is nothing to match up.

• •Flange kit: a flange head bolt and a flange nut. The flanges spread the load, so no washer is needed, and the zinc plated 4.6 flange bolts are threaded right up to the head for small grip ranges (Hobson's purlin flange bolt sheet; the M12 x 82 has a 30mm thread).
• •Hex kit: a hex head bolt, a nut and two washers.
• •Shoulder kit: a class 4.6 shoulder head bolt (16mm shoulder, 5mm deep, on the M12), a class 5 nut and a flange washer.
• •Class 4.6 kits pair a property class 4.6 bolt with a class 5 nut; class 8.8 kits pair an 8.8 bolt with a class 8 nut.

How to choose a purlin bolt

• •Size, class and number of bolts: from the shed or purlin supplier's design or the engineer. A purlin connection is structural, and Hobson publishes no joint capacity for these kits, so do not swap a 4.6 kit for an 8.8 (or the other way round) without that design saying so.
• •Length: long enough to pass through every ply of the joint and fully engage the nut.
• •Holes: Hobson's data sheets say hole size and dimensions should be to AS 4600 or as the designing engineer specifies.
• •Finish: see the finish section below; it depends on whether the bolt is inside the building or out in the weather.

Purlin bolt sizes

Select a row to open that kit in the selector, then pick the length.

How tight should purlin bolts be?

Use the tightening torque from the specifying engineer or the purlin supplier. Where they give none, Hobson's purlin bolt data sheets give the indicative torque below as a guide to setting a suitable one.

Conditions on these figures, from the same sheets: the torque is worked out to give a bolt tension of 50% of the bolt's proof load, using a torque-friction factor of 0.22 for zinc plated and 0.25 for hot dip galvanised assemblies; that factor varies with thread condition, lubrication and site conditions; the head and nut (or washers) must sit in full contact with the parts, with the bolt square, not skewed; and the required tension and torque should be checked and set by the deciding engineer.

Galvanised or zinc plated purlin bolts?

• •Zinc plated: Hobson rates it low corrosion resistance, for indoor and non-corrosive environments. Hobson's corrosion guide allows zinc plating only for enclosed fixings (inside a fully enclosed building) in very low and low corrosion zones.
• •Hot dip galvanised: Hobson rates it high corrosion resistance and recommends it for long term outdoor use. The corrosion guide lists hot dip galvanising or stainless for exposed fixings in low, coastal and industrial zones, so use galvanised kits on open sheds, carports, verandahs and anything out in the weather.
• •Seaspray zones and pools: Hobson's corrosion guide calls for 304 or 316 stainless for sheltered and exposed fixings in seaspray zones, and 316 stainless within 2m of a pool edge in every exposure; this range has neither. Ask us. In the coastal zone (away from seaspray), the guide accepts hot dip galvanising for exposed fixings.

Purlin clips and hangers

The purlin clips and hangers on this page fit to a purlin to hang threaded rod from a steel roof frame; Hobson lists them for cable tray support systems. The purlin clip has a captive thread (M8, M10 or M12) that the rod screws into. The D purlin hanger has a plain hole (9, 11 or 14mm) for the rod. The vertical hanger clip is a thin steel clip with two holes, sized 1.6-2.5 in Hobson's listing.

Hobson publishes no load rating for these clips and hangers. What hangs from them, and how far apart, needs a rated support system or the services designer's or an engineer's specification.

Fitting purlin bolts

1. Line up the holes in the purlin and cleat. Hole size to AS 4600 or the engineer's drawings.
2. Push the bolt through, with the head and nut (or washers) bearing flat on the steel.
3. Run the nut on and tighten to the specified torque, or Hobson's indicative torque where none is given, with the bolt square to the joint.

Purlin bolts in Adelaide

Allmat supplies purlin bolts, purlin clips, threaded rod and roofing screws to shed builders, steel fabricators, roofers and trade across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.

Questions