The Montana X-Treme Heavy Duty Bore Brush offers superior quality at an affordable price. These brushes are made with very stiff, heavy duty bristles and a solid brass core to assure your firearms will get a superior cleaning with minimal effort. The stiff bristles resist ammonia and oil-based cleaners. All brushes are 8-32 male thread except 17 caliber. The 17 caliber brush is 5-40 male thread.