0.5*4″barrel nipple

a pipe fitting with male threads on both ends and a straight, cylindrical shape. Here’s what each part of the term means:

1. 4″ Length: This indicates the length of the barrel nipple, which is six inches. This measurement refers to the distance between the two threaded ends of the nipple.
2. Barrel Nipple: A barrel nipple is a type of pipe fitting with male threads on both ends and a cylindrical or barrel-shaped body. These nipples are used to connect two female-threaded fittings or pipes together, providing a straight extension between the two components.

So, a 4″ barrel nipple would be a pipe fitting with a length of six inches, featuring male threads on both ends, and used to connect two female-threaded fittings or pipes together in plumbing system