ACL Performance Race Bearings are manufactured with a tri-layer metal with a hardened steel backing in order to withstand high RPM conditions, high stress loads, and high temperatures. Each ACL race bearing design features the following Large chamfer to accomodate larger crankshaft fillets 3&474 groove to provide optimum oil supply to rods and to maximize load carrying capacity Incresed crush and tighter wall tolerance for better seating Improved overlay and reduced thickness for increased fatigue strength Hardened steel backing to maintain crush under high loads and temperatures Size STD Note Pictures may not be actual product. HX Series Bearings are .0005" thinner per half to give .001" extra clearance for standard sized cranks.