A lock connects the distal end of a liner to the distal end of the hard socket of a prosthetic leg, and limits or prevents air flow into the hard socket through the distal lock mechanism, even when vacuum is established inside the socket. The distal lock normally is latched, but can be conveniently unlatched by swinging a cammed latch handle. The liner pin may be inserted and locked into the distal lock, without the distal lock being unlatched and without losing the internal air seal preventing air flow through passages of the lock. A slidable, biased lock blade, and interaction between slanted surfaces of the blade and the liner pin, allow the pin to slide down, but not up, past the blade. The latch handle does protrude radially outward a significant distance, when the lock is unlatched, but, as soon as the lock is latched, the handle resides against and/or near the outer surface of the lock housing.
