All Rotora high-performance replacement rotors are double disc ground to ensure parallelism. They are CNC machined and mill balanced to prevent vibrations. All rotors are e-coated (black) to prevent corrosion and prolong durability. Rotora? ?ï¿½ ? s high-quality and stringent quality control specifications assure that every component meets and exceeds worldwide ISO 9000 quality standards.All Rotora rotors are O.E. replacement rotors. They bolt directly onto your car with no modifications necessary to anything!We are often asked if slotted and/or drilled rotors are worth the additional money. The answer is yes! The reason is science.When you apply your brakes you are squeezing your brake pad to your rotor to create friction and as we know friction creates heat. This heat is in the form of a gas. The more friction the more heat, the more heat the more gas. The more you brake, the harder you brake, and the longer your brake all build up more hot gas.On a standard rotor this hot gas has no easy route to escape. The result is your brake pad is pushed away from your rotor so the gas can move. Now you can't stop as quick because your pad and rotor are being separated by the gas that needs to escape. This is commonly called brake fade.If you have slotted and/or drilled rotors then the hot gas has a channel to escape through and you will not experience brake fade as quick or for as long.The hotter a rotor gets and the more time it takes to cool off the more it warps. A solid rotor gets hotter and takes longer to cool off, thus warping quicker and requiring a replacement significantly sooner than a slotted and/or drilled rotor.When do you buy slotted?Slotted rotors are best suited for auto-cross and / or road-race competitors. They do not cool quite as quickly as a drilled or combination rotor, but they handle the additional stress of auto-cross or road-racing better than drilled rotors and thus last longer.Price is per rotor. Please order 2 for a pair.