The contact behavior between camshaft and follower is effected by pressure, lubrication and temperature. Regarding the camshaft, steel is the usual material for Heavy Duty Diesel engines, but also chilled ductile iron can be applied. There is a greater variety in design and material of the follower. For gliding contact chilled cast iron tappets offer an optimal compromise between performance and price; for higher loading, steel is a suitable material. A roller-tappet is required for maximum load conditions; if gliding contact is essential, carbide metal plated steel tappets can be used. Important design features for the roller tappet are concerning the pushrod pan, the roller chamber, the bearing between roller and pin and the prevention of twisting.