McJ Tools Reloading Bronze Bore Brushs are designed to meet or exceed military specifications, thus to satisfy the shooter who wants the best tools to maintain his or her guns. All brushes are 8-32 threaded. Each brush contains the maximum number of bristles that can be inserted for the caliber. Bristles are made from high quality bronze, which is aggressive enough to scour away lead fouling, copper fouling, and power residue. it will not scratch or in any way harm the bore.