Master Cylinder & Prop Valve DISC / DISCGM Style Disc Disc master and Disc Disc Proportioning valve .. ideal for doing the 60's 70's Style GM US style disc conversion final fitout or when changing to a Disc rear from Drum rear using a GM 70's Style disc conversion kit. Remember not all MC's or PV's have the same operational ability.. if you have some monster rotors with monster calipers etc.. you need their parts. This is otherwise ideal for stated purpose. ALSO BUY A PVTOOL if you don't