Bore Tech"s Proof Positive Nylon Bore Brushes have twice the amount of bristles compared to the competition, resulting in double the scrubbing action and faster cleaning. These brushes feature oversized bristles for extra rigidity and non-brass cores and couplers which prevent false indication of copper fouling remaining in your bore.The 17 - 20 caliber brushes are 1 in length and the 22 - 50 caliber brushes are 2-1/2 in length.Specifications:- Core Material: Steel- Core End: Rounded- Bristle Material: Nylon