How to measure U Bolts

Three numbers identify any U bolt: the inside width (the pipe or tube it fits around), the inside length (how far the legs reach through your plate or bracket) and the diameter (the rod and thread size). Every U bolt we stock ships as a pre-packed set with its matching nuts, so once those three numbers line up, you have everything you need.

Round U Bolt

Square U Bolt

Step 1  -  Measure the inside width

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. Working from the pipe instead? Measure the pipe's outside diameter and pick a U bolt whose inside width matches or just clears it - the width is printed in every product name (e.g. '40mm Inside (W)').

Step 2  -  Measure the inside length

Measure from the inside crown of the bend down to the end of one leg. This is the length that passes through your backing plate or bracket - both legs are the same, so measure one. If the cut end is chamfered, measure to the last full thread for the working length. Round U bolts wrap further around the pipe, so their usable leg length starts lower than a square bolt of the same overall size.

Step 3  -  Measure the diameter

Measure across the outside of the thread. Expect the reading a touch under the nominal size - an M10 U bolt reads between about 9.7mm and 10mm across the thread, an M12 between about 11.7mm and 12mm. Match it to a metric size (M6, M8, M10, M12, M16, M20) or an imperial size (1/4", 5/16", 3/8"). 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.

Step 4  -  Check what is in the pack

Round and square U bolts ship with two matching nuts; Round with Plate sets add the backing plate and crimp saddle. Some listings also include washers and some do not - the product name and description state exactly what ships in the pack. There is nothing else to order separately - just match the finish across your assembly (galvanised with galvanised, stainless with stainless) so the nuts run freely on the thread.

Browse the full range of U bolts. Still not sure which U bolt you have? Contact us and we will match it for you.