U-bolt

It is a bolt in the shape of the letter U with threading for screw on both the ends.

U-bolts have been used basically to support pipework, pipes through which fluids and gasses pass. As such, U-bolts were measured using pipe-work engineering speak. It described by the size of pipe it was supporting. They are also used to hold ropes together.

The nominal bore of a pipe is actually a measurement of the inside diameter of the pipe. Engineers are interested in this because they design a pipe by the amount of fluid/gas it can transport.

As U-bolts are now being used by a much wider audience to clamp any kind of tubing / round bar, then a more convenient measurement system needs to be used.

Four elements uniquely define any U-bolt:

1. Material type (for example bright zinc-plated mild steel)
2. Inside height (for example 110 mm)
3. Inside diameter (for example 30 mm – the distance between the legs)
4. Thread dimensions (for example M12 * 50 mm)