A U-bolt is a bolt in the shape of the letter U with screw threads on both ends. U-bolts have primarily been used to support pipework, pipes through which fluids and gasses pass. As such, U-bolts were measured using pipe-work engineering speak. A U-bolt would be described by the size of pipe it was supporting. U-bolts are also used to hold ropes together. Size: M6 to M20
