Until relatively recent years, the primary method of transmitting torque from a prime mover to driven machinery was through the use of a mechanically actuated dry friction clutch. Without a skilled operator, the reliability of these clutches suffered. Improper adjustment, maintenance, and overall abuse led to increased wear and ultimately failure. As knowledge of materials and manufacturing processes grew, the precision and reliability of these clutches increased, yet, they still left end-users frustrated. In light of perpetual frustrations, and a lack of skilled operators, mechanically actuated dry friction clutches have been replaced by other devices such as hydraulically actuated wet friction clutches, fluid couplings, and torque converters and hydrostatic transmissions.