StopTech Sport Rotors are also available with an optional cryogenic treatment. Although cryogenic treatment is invisible to the naked eye; many fleet customers are sold on its ability to extend the service life of the brake rotor. Deep cryogenic treatment is a one-time process that permanently improves the performance and wear characteristics of metal components; from brake rotors and engine parts to machine tools and gear sets. All new StopTech Sport Rotors may be ordered with cryogenic treatment for an additional fee.Symmetric vane; split-core castings for uniform heat distribution. Black E-Coat anti-corrosive coating protects much better than competitors spray paint. Double disc ground friction surface for optimal performance and service lifeThis extra process provides better rotor balance and creates a cleaner; more finished looking component; In addition; Rotors are inspected for balance and mill-corrected to a tolerance of less than 2oz2001 2005 BMW 320i, 2000 2007 BMW 330Ci, 2000 2005 BMW 330i, 2000 2005 BMW 330xiBlack E-Coated Non-Friction Corrosion ProtectionDouble Disk Ground For Consistent Friction SurfaceSuperior Resistance To Cracks From Thermal StressDirectional Curve Vane Designs On Selected AppsIncreased Initial bite and Wet Weather ResponseCryogenic Treatment Reduces Residual StressSlots Helps Evacuate Gasses/Dust/HeatDirect OE Replacement