The clutch sprockets commonly used today were designed by SMC in 1995.

Prior technology was a steel sprocket welded to a steel drum. SMC figured out how to connect a steel sprocket to an aluminum drum for the sake of lighter weight, lower cost and most importantly, better heat dissipation.

Caution: other manufactures have copied the SMC sprocket geometry but not its precision, durability or engineering expertise. If you want a sprocket of the highest quality at a fair price, choose SMC brand clutch sprockets.