Brake Booster:7" Zinc Single Diaphragm brake boosterIdeal for most small to mid size street rods and customs.The booster mounts with a 4-bolt pattern.The 4 bolts are in a perfect square and are 3 3/8" apart (center to center).The booster requires 18" of vacuum to operate properly.With this vacuum level the booster will produce a maximum pressure output of 950 psi with a 1" bore master cylinder.This pressure level works well for four wheel drum systems and disc/drum vehicles which are relatively light.Master Cylinder:GM Universal Cast Iron 1" Bore; 9/16" & 1/2" Ports on Both Sides RawWorks for Disc/Drum, Disc/Disc or Drum/Drum Applications1" Bore, 9/16" & 1/2" Ports on Both Sides W/ Plugs for unused portsIncludes plunger for Deep or Shallow BoreFor use with Manual or Power brakes