The same high-quality steel part that Springfield uses on their handguns. It offers a positive slide lock hold open on last round. The slide stop shelf is serrated for a positive, non-slip slide release. Drop-in fit, no gunsmithing required. Parkerized.Most 1911 users view this as a desirable feature because you can chamber another round and be ready to go just by inserting another magazine and releasing the slide stop. However, when competing with 2011 style guns there are some disadvantages to this system – enough so that I prefer to disable this feature in the competition guns I build.