Brass 2-1/2"x4" Nipple. Brass Pipe and Fittings are manufactured for both commercial-industrial and residential standards. Brass has a high level of tolerance, making it ideal for oil, water, and air line applications. Brass fittings are universal, they can be used by professionals and DIY guys. This Brass 2-1/2"x4" Nipple is a pre-cut section of pipe designed to speed up the connection process. When brass pipe is cut, in generally has to be threaded also. This nipple allows you to remove both the cutting and threading and add the nipple anywhere a small connection piece is needed.