3/8" x 3/8" compression tee, quiet pipe, hammer arrestor, helps solve current & potential water hammer problems, use a piston design to help absorb the water shock in the system, when a valve is closed abruptly, the water moves into the pressurized chamber of the hammer & the water pressure is absorbed to prevent banging within the pipeline, once the water flow comes out of the chamber, it is dissipated to the rest of the water line.