Otis Bulk 10 Pack No.50 Brushes (50 Caliber, 12.9mm) 10 pack, bronze bore brushes . 50 caliber Brush has tufor proprietary core Wire Includes: reusable snap-pack case Superior construction and engineered features Reusable snap-pack case Corrosive resistant Twice the fill as other brushes Specific caliber stamped on the stem