The self-locking pulley is especially designed for rescue operations. It features a brake cam system which allows the rope to go through freely in one direction and blocks it in the other direction. The spring-loaded cam can be disengaged by pulling a release cord. When used in a system (with a matching double pulley), it provides 4:1 mechanical advantage. Both 62 mm (2-1/2'') diameter aluminum pulleys are mounted on self-lubricating bushings and stainless steel axles. The swing sides and the main plate are also made of anodized aluminum.