Stop collars let you drill at exactly the depth you want. Just place the collar over the drill bit & tighten the set screw to lock the collar. Eleven popular sizes to choose from. The #8000 set contains the seven most popular sizes:1/8”, 3/16”,1/4”, 5/16”,3/8”,7/16”, and 1/2”. The #8001 set is the larger size collars: 5/8”, 3/4”, 7/8”, & 1”.