2001- Later GMT800, 2500HD, 3500 with 6.6 liter Duramax diesel engine GM-44643 is used to hold the flywheel/engine stationary during removal of the hub bolt. The bolt must be removed in order to service the pulley assembly. Locate and remove the starter unit. Place GM-44643 in the location where the starter normally mounts. Secure GM-44643 in position with bolts (not supplied with the tool)