U-Bolt

What U-bolts are used for

A U-bolt is a bar bent into a U with a thread on both legs. It wraps around a pipe, tube, post or section and passes through a plate, bracket or crosspiece, and nuts on both legs clamp the lot together. They suit pre-drilled or pre-punched holes.

Common uses: clamping pipe and tube to frames, mounting brackets, signs and antennas to poles (U-bolts used this way are often called pole clamps), fixing square posts and RHS to rails and frames, and tractor and spreader bars. Hobson also lists trailers and cast-in anchors in concrete among the uses for the 316 square spring washer kits, but it publishes no load rating for any of these U-bolts, so an anchor, trailer axle or suspension joint that carries load needs a rated product to the designer's or maker's spec.

Round or square U-bolts?

• •Round bend: a curved U that wraps a pipe or round tube. Sized by the pipe it fits, in nominal bore (NB): a 25NB U-bolt fits 25NB pipe.
• •Square bend: a U with square corners for square and rectangular sections: square posts, RHS beams and columns, and square timber. Sized by inside width and leg length.

How to size a U-bolt

Hobson sizes U-bolts by A (the thread), W (the width measured between the legs, inside), L (the leg length) and T (the length of thread on each leg). For a round U-bolt, NB is the nominal bore name of the pipe it fits; the tables also give W, so you can check it against the actual pipe, tube or pole.

Measure the outside of your pipe, post or section and choose the W that fits it. Then check L is long enough to pass through your plate or bracket with thread left for the washer and nut.

Round U-bolt sizes (metric)

Round U-bolt sizes (BSW)

Square U-bolt sizes (metric)

Square U-bolt sizes (1/2 inch BSW, galvanised)

What comes with each U-bolt

• •Galvanised and zinc plated round kits (metric and BSW): the U-bolt and 2 nuts. The M12 40NB galvanised round kit comes with a nut and washer.
• •Galvanised and zinc plated M10 x 42 square kits: the U-bolt and 2 nuts.
• •Galvanised metric square kits (M10 x 24 x 60 and the M12 range): 2 nuts and 2 spring washers.
• •1/2 inch BSW galvanised square kits: a Nyloc nut and washer.
• •316 stainless M12 square kits: supplied with spring washers. Hobson does not list the contents of the 316 round kits or the M10 316 square kit, so ask us if you need to know.
• •1/2 inch BSW galvanised square U-bolt only: no nuts. Add the parts your job needs, such as Nyloc nuts, hex nuts, spring washers or wedge locking washers.

Galvanised, zinc plated or stainless U-bolts?

• •Hot dip galvanised: a thick zinc coating (about 50 microns) with high corrosion resistance, recommended for long-term outdoor use.
• •Zinc plated: a thin (about 5 micron) coating with low corrosion resistance, for indoor and non-corrosive conditions.
• •316 stainless: corrosion resistant right through. It stays bright when it is washed by rain or kept clean, but it is not made for sitting in seawater.

How to fit a U-bolt

1. Choose the U-bolt whose W fits around your pipe, post or section, and whose legs are long enough for your plate plus washers and nuts.
2. Hold the U-bolt against the plate or bracket and mark both holes, then drill them to suit the thread size.
3. Fit the U-bolt around the pipe or post and through the holes.
4. Fit washers and nuts, and tighten the two nuts evenly, a little at a time, so the plate sits square.
5. Where the joint will see vibration, the Nyloc nut kits or spring washers help stop the nuts working loose.

Load ratings

Hobson publishes no load ratings for these U-bolts. For clamping a trailer axle to its springs, use U-bolts made and rated for that job, to the trailer or axle maker's spec, and for any other engineered joint use parts rated for it.

U-bolts in Adelaide

Allmat supplies U-bolts, nuts and washers to builders, fencers, plumbers, farmers and fabricators across Adelaide and South Australia. Add the U-bolts to a quote with the rest of your list, and we will price the lot.

Questions