a mill cutting structure is differently configured in three zones . those zones are the center , the outer edge and in between . at the center has highly wear resistant material that has good temperature bond strength and high impact resistance . the outer periphery can have a material that is highly resistant to wear and impact . in between can be inserts such as used in the metal muncher ® mills using sintered carbide shapes that resist tracking and create a chipping rather than a grinding action . the shapes should have high edge retention capability and shapes such as a double sided pyramid can be used . the wear patterns of prior designs are addressed to allow longer and faster milling of the fish .