77-98 YAMAHA YZ250: Sunstar Front Sprocket (520 / 14T) Sunstar is the largest O.E.M. supplier of sprockets and brake rotors in the world. In fact, your motorcycle probably came from the factory with a Sunstar sprocket. Need a reason to choose Sunstar? Every Sunstar product is imbued with superior quality, uses an exclusive heat-treatment and quenching process, is based on advanced research and design, and is sold at an added value price. Manufactured from case-hardened chromoly steel for the ultimate in strength and durability.