Hardened tempered chrome-plated corrosion-resistant chrome vanadium. Chamfered end for positive nut location, with rubber inserts for plug retention and protection. Includes 16 and 21mm spark plug sockets. Hardened tempered chrome-plated corrosion-resistant chrome vanadium. Chamfered end for positive nut location, with rubber inserts for plug retention and protection. Includes 16 and 21mm spark plug sockets.