BoreSmith, Gauge 20, Shotgun Bore Brushes, 10-Pack, Phos Bronze Our standard brushes have phosphor bronze filaments, and they are made for shotgun length chambers Standard 5/16-27 threaded connectors are made of non-abrasive aluminum Carbon-steel twisted core wires give our brushes superior strength that resists bending Comes packed in clam shell for safe and easy storage Phos bronze filaments clean with more friction than nylon filaments do