This is a Billet Steel Timing Chain Sprocket designed with the same dimensions as the original Toyota RZ sprocket. We produced the lower sprocket from billet steel since the original simply cannot provide the strength necessary when you increase the HP of the engine. The original powdered steel material is reduced around the keyway and makes the original unit weak and can destroy your high performance engine. Once the sprocket breaks at high RPM, it will destroy your valvetrain and cams. Our Billet Sprocket can provide the strength needed and peace of mind that this item will not break. We have been using them for years and supply them for many race teams and high HP RZ engines around the world. Buy them direct at the best price here.