GM Cast Iron Master CylinderBore: 1"Disc/Disc ApplicationsDeep PocketDual Reservoir4 Ports Dual Reservoir Master Cylinder features GM ports on both sides, a sturdy cast iron body, with a tough cast iron finish. The oval-shaped lid is finished in yellow zinc and is fastened with a two bale wire straps. This unit is has a clean, classy look that will be a welcome new addition to any engine compartment. There are four ports and the bore diameter is 1". Enjoy plenty of strong braking power! Use dot 3, 4 or 5 fluid.