MSR/AR-15 rifle owners know the importance of a clean bolt and bolt carrier group. Carbon and fouling can build-up in these areas, causing jams and malfunctions. The B.O.N.E. Tool was designed specifically to clean the bolt carrier assembly area of .223 Rem/5.56mm NATO rifles. Otis Technology BONE Tool FG246. Scrapes carbon and fouling from the Bolt, Bolt. Carrier and Firing Pin. Threaded hole is 8-32. Can act as a T handle.