FITTING, Vacuum Port, rear, repro, on intake, 3/8 npt thread, Has booster fitting and 3 vacuum ports, Can also be used on A/T cars converting to power brakes with a 3/8 inch npt thread size at the intake manifold, The large nipple (3/8" O.D. tube diameter) is for the booster and the smaller (1/4" tube diameter (1) and 3/16" O.D. tube diameter (2)) for the transmission modulator hose, distributor vacuum advance, intermittent wipers, vacuum hide-away headlights, heater or A/C etc , Can also be used on M/T cars for the booster if the extra ports are plugged.