40A20 Type "A" sprockets are hubless sprockets with a stock bore. Nitro 40A20 sprockets are made to the ANSI B29.1 standards. These are also commonly referred to as plate sprockets. Our 40A20 sprockets are manufactured from 1045CD carbon steel and have a black oxide finish. The teeth are hardened to help minimize tooth wear. Type A sprockets are great for welding onto shaft for machining in bolt holes for mounting.