i believe it's around .020-.030
For a GM product that would be the norm, but Chrysler's seem to work well with .060 (1/16 inch) clearance......
thanks for the clarification.
after flipping through a couple of FSM's, all i could find was the booster rod length from the master cylinder mounting surface at the booster to be .910-.920. there was no mention of clearance between the booster rod and the master cylinder piston bore depth.
not having a master cylinder handy to measure the piston bore, i didn't have a reference.