Promax C-1 chain tensioners are extruded then CNC-machined from 6061-T6 aluminum for optimal strength and low weight. When used properly, they will protect your frame dropouts and help hold your rear wheel in place CNC-machined 6061-T6 aluminum For use with 3/8" and 10mm axles Two axle hole design ensures adjustability on most frames Sold individually (Each)