0.75″Gi barrel nipple

a plumbing component made of galvanized iron (GI) with specific dimensions and characteristics:

1. Size: The “0.75 inches” dimension indicates the diameter of the nipple, which is three-quarters of an inch. This measurement refers to the diameter of the threaded portion of the nipple..

So, a 0.75″ GI barrel nipple is a galvanized iron pipe fitting with a diameter of three-quarters of an inch and a barrel-shaped body, used to connect two female-threaded fittings or pipes together in plumbing systems.