U-bolt is a letter U-shaped fastener, with two threaded arms (or legs) stretching from a curved base. G.I. U- bolt have screw threads on both ends to ensure the pipe stability.  U-bolts have primarily been used to support pipework, pipes through which fluids and gasses pass.
 

Size	1/4 x 1/2  - 3/8  x 8
Material	Steel, Stainless Steel 304 (A2), Stainless Steel 316 (A4)
Application	U-bolts are usually used in the support of pipes or in the connection of a component on a pole, beam or wall, where “u” form maintains them firmly, adding to the support stability.