Hex Bolt & Nut (XL Thread)

Long galvanised bolts and nuts with an extra long thread

These are commercial hex head bolts in class 4.6 to AS 1111.1, hot dip galvanised and supplied assembled with a class 5 galvanised nut to AS 1112.1. Hobson calls them XL bolts because the thread runs much further up the shank than on a standard bolt: an M12 x 100mm XL bolt has 70mm of thread, where the general formula for a standard bolt gives 30mm. With more thread the nut can run further down the bolt, so one length clamps a wider range of thicknesses.

Lengths run to 1500mm in M16, M20, M22 and M24, long enough to go right through posts, sleepers, stacked beams and thick timber. Common jobs are through-bolting timber posts, sleepers and beams, and farm, fencing and general construction work. For any structural joint (deck and pergola framing, posts), Hobson publishes no joint capacity for these bolts: the bolt diameter, grade, number and washers come from AS 1684, the span tables or the engineer's design.

Extra long thread vs a standard bolt

Hobson's bolts and set screws article gives the general formula for a standard bolt's thread length, where D is the diameter: 2D + 6mm for bolts up to 125mm long, 2D + 12mm from 125 to 200mm, and 2D + 25mm over 200mm. Worked out for some XL sizes: M12 x 100mm, 30mm standard against 70mm XL; M16 x 300mm, 57mm against 110mm; M20 x 600mm, 65mm against 210mm; M24 x 1500mm, 73mm against 225mm. On the shorter lengths in M10 to M16 (M10 x 65, 75, 100 and 110mm, M12 x 50 and 60mm, M16 x 75 and 100mm) the thread is the same as a standard bolt's, and the M8 x 30 and the 25mm bolts are threaded right up to the head.

The trade-off: the same article explains that in a joint carrying shear the plain shank should cross the joint, because the threaded section has less shear area. With an XL bolt more of the length is thread, so check where the thread will sit in the joint. Where the design calls for a plain shank through the joint, use the bolt the design specifies.

Long bolt sizes and thread lengths

Every XL bolt and nut we carry, shortest to longest within each diameter. Lengths that share the same thread length are grouped into one row; select a row to open the shortest length in it, and pick the exact length in the selector. Bolt length is measured from under the head to the end of the bolt.

Spanner sizes

The bolt head and the nut take the same spanner. From Hobson's metric spanner selection sheet, AS 1111 and AS 1112 column.

Working out the bolt length

Add up everything the bolt passes through, the washers and the nut, then allow two or three threads past the nut. For example, a 90mm post between two 45mm beams with a square washer under the head and under the nut (3mm each) and an M12 nut (about 11mm), allowing 5mm of thread: 45 + 90 + 45 + 3 + 3 + 11 + 5 = 202mm, so an M12 x 220mm bolt.

Then check the thread: the M12 x 220mm XL bolt has 110mm of thread, so about 110mm of plain shank. The joint plus washers (186mm here) must be thicker than the shank for the nut to clamp, and it is. If the joint is much thinner than the bolt is long, pick a shorter length rather than relying on the thread.

Galvanised bolts and nuts: where they suit

Hot dip galvanising is Hobson's 50 micron, high corrosion resistance coating, recommended for long term outdoor use, and the nut is galvanised too. Hobson's corrosion guide for metal connectors gives the minimum protection by exposure:

• •Exposed to the weather, such as decks, pergolas and fences, outside the sea spray zone: stainless or hot dip galvanising, so these bolts meet the guide's minimum.
• •Hobson's guide covers exposure to the air only. Bolts in the ground or against wet soil, such as in sleeper retaining walls, are outside it, so the bolt and its protection there come from the designer.
• •Sea spray zone, sheltered or exposed: stainless. Within 2m of a pool edge: 316 stainless. These XL bolts are galvanised only; 304 and 316 stainless bolts are on the hex bolts page.
• •A dull, matt grey galvanised finish is normal. Hobson's article on it quotes the Galvanizers Association of Australia: the brightness of the coating has no effect on its performance; coating mass is what sets its life.

Long bolts and nuts in Adelaide

Allmat supplies long galvanised bolts and nuts, washers and threaded rod to builders, landscapers, farmers and fencers across Adelaide and South Australia. Add the bolts to a quote with your posts, sleepers and beams, and we will price the lot.

Questions