600140-03 is a flywheel kit for various Mazda RX-7 and RX-8 applications comes complete with an ACT counterweight. The flywheel counterweight is required when installing the XACT flywheel on various Mazda RX-7 and RX-8 rotary applications. XACT Prolite flywheels are ACT's lightest 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, lower inertia, good heat tolerance and rigidity. XACT flywheels are serviceable and can be resurfaced with no need to purchase additional parts.