Originally Posted by bubbahotep
Maybe my term is wrong. That's the little metal pin that the brake booster pushes into. It slides out easily of the master cylinder. It's not a piston, sorry
This piece is included in some master cylinders so that the same master can be used for power or manual brakes.
Manual brakes have a deeper bore in the piston to retain the brake pushrod.
Power brakes usually have a very shallow bore as the piston pin is retained by the booster.