This is our Specialty Diamond B40BIT which translates to a 1-1/2″ inch radius metal bond diamond router bit. It’s used in a stone router that has a standard M10 arbor. This bit is a coarse position 1 bit (about 20/30 grit) that is used to make the initial shape to your square cut granite or marble counters. Usually after shaping your counter you’ll want to come back over the fresh cut edge and polish it with a variable speed wet polisher up to your satisfaction.