The Nylon Brushes are constructed of a material that is unaffected by most modern powder and copper solvents. This resistance is a benefit over bronze brushes. The bristles are designed to be very ridged providing maximum bore scrubbing performance. Made from premium phosphor bronze for long life and cleaning power. Molded durable, hinge top storage box with marked slots included. Threads are industry standard: 8-32 on .22 cal through .45 cal.