12B-3 hardened hub sprockets have three tooth rims for triplex 12B-3 chain of 3/4" (19.05 mm) pitch to DIN 8187 / ISO 606. The teeth on all three rims are induction-hardened.
12B-3 hardened sprockets - longer life under very high torque
Three chain strands transmit very high torque, and hardened teeth extend sprocket life under such conditions. The C45 steel hub is not hardened, so you bore the hole out for your shaft and cut a keyway.
12B-3 triplex sprockets with hardened teeth
12B-3 triplex sprockets in C45 steel with teeth hardened to 45-55 HRC. 12B triplex sprockets with unhardened teeth can be found in the Hub sprockets group.
Questions and answers: 12B-3 hardened triplex sprockets
Can I combine a hardened and an unhardened sprocket in one drive?
Yes. A common practice is to use a hardened driving sprocket and a standard driven sprocket - both must have the same number of strands.
