The 4" three port junction fitting gives you the ability to attach up to three different machines or tools to one convenient fitting. Works great with tablesaws, jointers, planers, bandsaws and more! The fitting is designed to be used with 4" hose and requires the use of hose clamps (not included see page 26 for hose clamps and accessories). The three port junction fitting has a 4" O.D. and a 3-7/8" I.D. on all four openings.