600145-03 is a flywheel kit for various Mazda RX-7 and RX-8 applications and 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. ACT XACT Streetlite flywheels are considerably lighter than stock and are the most durable flywheel offering from ACT. Materials are properly distributed for maximum strength lower inertia good heat tolerance and rigidity. ACT's Streetlite flywheels are preferred for street or drag racing. XACT flywheels are serviceable and can be resurfaced with no need to purchase additional parts.