Full definition
Toothed wheel that positively engages a roller chain to transmit rotary power between shafts. Material: typically AISI 1045 carbon steel with teeth hardened by induction (50-55 HRC) for wear resistance while maintaining a tough hub. Standard tooth counts: 17-21 teeth minimum for smooth operation at moderate speeds; fewer teeth cause chordal action (speed pulsation) and accelerated wear. Per ANSI B29.1 and ISO 606. Types: Type A (plate only), Type B (one hub), Type C (two hubs). Must be replaced when tooth profile shows visible hooking. Brands: Martin Sprocket, Rexnord, Tsubaki, Browning. Always replace chain and sprockets together for best life.