Hoppe's Universal Bore Guide is a simple tool that makes a big difference when cleaning a firearm. It prevents bore cleaners from dripping into the action of a firearm while also preventing excessive contact of the cleaning rod with the inside of the barrel near the chamber. The threaded brass pin locks the guide into the action instead of the bolt to allow proper cleaning of the bolt. Our bore guide comes with three interchangeable chamber tips to accommodate from a .17 caliber to a .416 caliber, and the aluminum collar fits bolts of 0.695"/0.700" (17.65 mm/17.78 mm) diameter of any action length.