These Thompson/Center Arms bolts are factory replacements for the Dimension modular rifle system. The Dimension rifle system allows the shooter to determine what caliber is needed for the current situation and then switch components to create the most suitable platform. This allows one rifle to take game ranging from prairie dogs to moose, and any species in between. Each bolt is stamped with the letter corresponding to the series of parts that coincide with that particular caliber. The user simply chooses the barrel and magazine with the same letter. Use the Thompson Center Torque Tool, product 169204, to tighten the barrel. Once assembled, the rifle is ready for the next hunting adventure.