Smooth Idler Pulley, LB7 LLY LBZ LMM LML, 2001-2016 Duramax

This does not have the ribs on it for running on the inside of the belt 

Hearing a noise under the hood?  Check those idler pulley's carefully.  Any noise in them could be a sign that the bearing is going bad.  A failed idler pulley will usually cause the belt to come off, leaving you stranded.  Don't get stuck on the side of the road for the price of this pulley. 

02 and newer Duramax engines use 2 of these.