GM offers three different thickness head gaskets for its GM 6.6L Duramax diesel engines depending on the amount of piston protrusion the engine has. When measuring piston protrusion, make sure that you measure all pistons on each bank.
See Figure 1, for gasket grade mark location and bank location on the gasket. For the maximum value of protrusion for each bank, determine the proper gasket using the information from Figure 2.
Notice: The left and right cylinder head gaskets are not interchangeable. Improper placement of the cylinder head gasket will block coolant and oil passages and oil passages and will cause severe engine damage. The gasket markings face up when correctly installed.