FOR GM 604 CRATE ENGINE RECOMMENDED FOR MAHLE CRATE 604 PISTON-. OVER SIZE Bore (in):4.000 PLUS,  in. Bore (mm): 101.600mm File Fit: Yes Top Ring Included :Yes Top Ring Thickness :2.0mm Second Ring Included: Yes Second Ring Thickness :1.5mm Oil Ring Included: Yes Oil Ring Thickness: 4.0mm Oil Ring Tension: Low Oil Ring Tension Rating: 11 lb. Gapless: No Top Ring Material: Ductile iron Top Ring Facing Material: Plasma-moly Second Ring Material: Cast iron Second Ring Facing Material: Cast iron Oil Ring Material: Stainless steel Quantity: Sold as a set. Total Seal CR Classic race piston rings are built around Total Seal's ductile iron, plasma-moly coated conventional top rings. They have conventional cast iron second rings and 3-piece, standard-tension stainless steel oil rings. These ring sets are ideal for street use, race applications, and mild levels of nitrous or forced induction.