the hammer and the sear, but a lot of them are not to spec, so the safety only engages the sear. If you cut off the engaging lug of the grip safety, you can remove it without bothering to remove the mainspring housing. Thats handy when you've installed setscrews thru the frame and into blind holes in each side of the Mainspring housing. this setscrew mod prevents tearing out of the frame, below the MSH pin, and is highly recommended for guns use for hot loads, especially alloy frames.