600555 is a Prolite flywheel, which is ACT's lighter flywheel offering with lowest inertia. Prolite flywheels are designed for best throttle response and acceleration. Prolite flywheels are preferred for road racing or rally racing, and have reduced drivability. Materials are properly distributed for maximum strength, good heat tolerance and rigidity. ACT flywheels are serviceable and can be resurfaced with no need to purchase additional parts.