1. StopTech SportStop slotted rotors are machined with slots crossing the vanes, not parallel to them.
2. Unless the vehicle manufacturer specified otherwise, rotors with directional vanes are to be installed so that at the top edge of the rotor, the vanes sweep toward the back of the car.
3. StopTech SportStop slotted rotors with non-directional vanes, or solid rotors, are marked right or left so as to be consistent with rotors following rules 1 and 2.
4. Slots perform their function identically regardless of direction. Only in the case of "straight" vane or solid rotors, if a customer prefers the appearance, rotors may be installed with the slot direction reversed.
5. Certain OE applications use a single, directionally-vaned part number on both sides of the car. In those cases, the slot direction will be different on each side of the car. If that is unacceptable, consider Centric Parts 120 Premium Series smooth-faced rotors.