Steel pipe coupling is a very short length of tube used in piping or plumbing, it usually refers to the socket weld or a threaded on one or both ends that allows two tubes connected together.
Threaded socket is commonly called threaded coupling and used to connect with the steel tubes. There are two mainly threads which are BSP and NPT.
• For use in air, water, and natural gas applications
For stainless steel coupling material standard is ASTM A182, grades in F304/L or 316/L. Stainless Steel coupling has a higher better corrosion resistance.