Our durable black iron fittings are pressure tested at the factory and are dipped in rust preventative. The 1/2" x 2" black nipple is for use with above ground gas, LP and air applications, and is not for not for use with potable drinking water or in underground applications. They are threaded on both ends with standard taper pipe threads conforming to the American Standard for Pipe Threads A.N.I.S. B1.20.1. The threads are right hand on each end and the nipples have a length tolerance of plus or minus 1/10". Always check your local plumbing and gas codes before starting any piping projects.