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Technical Resources
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Square

Square
"
Not sure what size U bolt you have or need?
Two ways to confirm before you order - whichever you already know.
1If you have the pipe or tube

Measure the outside diameter of the pipe, tube or shaft, then pick a U bolt whose Inside Width (W) matches or just clears it. The W value is printed in every product name (e.g. '40mm Inside (W)'), and the Length (L) is the leg length that passes through your plate or bracket.

2If you have a U bolt in hand

Three numbers identify it: the inside width between the legs (measured across the straight section, not the bend), the leg length from the crown down, and the diameter across the thread. Our step-by-step guide shows all three with drawings.

Open the U bolt measuring guide ›

U bolt drawing showing the three measurements

About Square U Bolts

Square U Bolts are bolts with a 90-degree square bend, designed to clamp square or rectangular hollow section (RHS / SHS) or angle to a structure. The square bend matches the flat face of the host section for full-contact clamping, where a Round U bolt would only contact at two narrow tangent lines and crush the corners under load.

Every Square U Bolt SKU on the BNA store ships as a pre-packed set with two matching nuts and washers - nyloc nuts with flat washers on most SKUs, or hex nuts with spring washers on the rest. Check the product page for the exact pack contents.

How to Measure

Three quick measurements identify any U bolt: inside width (W), leg length (L), then rod diameter and thread pitch.

Step 1 - Inside width (W) With the U bolt sitting on a flat surface, measure the gap between the inside faces of the two legs. Measure across the straight section of the legs, not at the bend - the bend reads a little wider. This is the maximum diameter of pipe, tube or shaft the U bolt will clamp around.

Step 2 - Leg length (L) Measure from the inside crown of the bend down to the end of one leg. This is the length of the U bolt that passes through the backing plate or bracket. Both legs are the same length - measure one. If the cut end is chamfered, measure to the last full thread for the working length.

Step 3 - Rod diameter and thread Measure the diameter of the rod across the unthreaded shank (not the threads - the thread crests sit slightly proud of the rod itself). Match the diameter to a metric size (M6, M8, M10, M12, M16, M20) or an imperial size (1/4", 5/16", 3/8" etc). The thread pitch follows the standard coarse pitch for that diameter (M10 is 1.5mm, M12 is 1.75mm) unless the part is marked otherwise.

Still not sure? See our step-by-step identification guide for help measuring your fastener.

Technical Resources

Every U bolt sub-category has its own CAD drawings and spec PDFs linked at the bottom of its page. For the full library covering U bolts and every other product range we stock, see our Technical PDFs library.

Frequently Asked Questions

Why use a Square U bolt instead of a Round one?

Square U bolts have a 90-degree bend that matches the flat face of square or rectangular hollow section (RHS / SHS). Round U bolts on a square host only contact at two tangent lines and crush the corners under load.

Square U bolts spread clamping force across the full face of the section, giving a more secure clamp without distorting the host.

What's included in the pack?

Every Square U bolt SKU ships as a pre-packed set with two matching nuts and washers - nyloc nuts with flat washers on most SKUs, or hex nuts with spring washers on the rest.

Check the individual product page for the exact pack contents. The supplied nuts and washers match the U bolt thread and finish.

Material & Coating

Galvanised Hot-dip galvanised carbon steel. The standard outdoor finish; thick zinc coating gives decades of corrosion resistance. The right choice for trailer chassis, mast and pole mounting, structural pipe clamping and outdoor tank fittings.

Stainless A2-70 G304 - the standard stainless grade. Suits most external Australian environments. Used in food, dairy, mining and general outdoor work. A4-70 G316 (marine grade) adds 2-3% molybdenum to resist chloride attack within 300m of the coast.

Zinc Plated Bright silver electroplated zinc - interior use only. Suits protected industrial applications, indoor pipe clamping and machinery-frame use.

Matching finishes Always match the finish across the assembly. Hot-dip galvanising adds a much thicker coating than zinc plating, so a zinc-plated nut will not wind onto a galvanised bolt, and a galvanised nut on a zinc-plated bolt will be loose. Pair galvanised bolts with galvanised nuts and washers.

Browse our U bolts — Round · Square · Round with Plate · Matching Nuts · Matching Washers

Need help picking a U bolt? Tell us the inside width (W), leg length (L) and diameter you need - we'll match the right SKU. Contact us or call 07 3192 9800.

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Square U bolts with 90-degree bend for clamping square or rectangular hollow section. Every SKU ships pre-packed with two nuts and washers - nyloc + flat or hex + spring depending on SKU.

TECHNICAL RESOURCES

Need help sizing your U bolt? See our U bolt measuring guide.

For the full library of charts and specs, see our Technical PDF's Library.

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