Double Roller Billet Steel Chev Mark IV 9-Keyway Double Roller Timing Chain Set These pro billet competition timing sets are designed for accuracy and long life. Lightweight by design these sets feature a CNC machined billet steel cam sprocket with lightening holes, a heat-treated crank sprocket with 9-keyways and a black oxide coating. The chain is a large .250” diameter seamless roller. Most sets include a press fit roller thrust bearing. Note: No machining required.