MBM-MC1321H-Universal Cast Iron Master Cylinder GM Universal / Corvette style Cast Iron 1" Bore Master Cylinder. 9/16" & 1/2" Ports on Both Sides; Exact Copy of Original; Master Cylinder has a piston adaptor that will allow for power or manual applicationsFor Disc/Drum or Drum/Drum Applications. (Note: if you are running Drum/Drum you will also need a metering valve PVM)