The ground-breaking MAC GT4 clutch is unlike any other soft-start clutch available for sport aircraft today.  The clutching element is a set of 10 each, 8mm diameter, hardened rollers that pinch between the inner saw-tooth hub and the outer smooth race.  When the rollers or races wear from use, they never stop engaging like centrifugal clutch shoes or sprag dogs do.  This makes these clutches the safest possible solution for coupling engine torque to the gearbox, while saving exhaust and frame work from rattling fatigue and cracking due to hard shaking experienced when starting the high-compression Yamaha, and other engines.  An added benefit is that the GT4 clutch winds up weighing fully less than half that of any other clutch available on the market.