Master cylinder help

The main difference is that the manual brake rod has a rubber bushing on the end to secure it in the piston. I think a manual MC piston has a step or taper to capture the bushing, though it might self-lock in just a smooth bore.

A manual MC also has tapped holes on the back to mount a piston retainer-rubber bellows, which usually comes on rebuilt MC's (often w/ the rod). The boot keeps dust from the passenger compartment from getting in the piston bore, though old ones usually split or fell off.

Also, a manual MC with a failed piston seal will usually spill brake fluid into the cabin, dribbling down the inner firewall and floor, removing paint, and causing rust. Power MC's dribble down the booster onto the firewall but not on my cars w/ DOT 5.