A coupling connects two pipes. If their measurements differ, the fitting is called a reducing coupling, reducer, or an adapter. There are 2 kinds of couplings: "regular" and "slip". An everyday coupling has a small ridge or cease internally, to prevent above-insertion of the pipe, and thus under-insertion of the http://valves-and-fittings41851.designertoblog.com/17886022/valves-and-fittings-an-overview