3/8" compression x 3/8" female compression, mini rester residential water hammer arrester, 3/8" od x 3/8" reverse nut tee, for 3/8" od compression stop valve for hot or cold piping, stops pipe banging, reduces strain on plumbing system joints, perfect for dishwasher connections, shall be installed where required on supply valves, specifically sized & have sufficient volume of air to dissipate the calculated kinetic energy generated by closing, code requirement in some southeast cities.