The EBC "GD" series is signified by a "three spot" drilling pattern and a wide aperture full width slot. The full width slot expels dirt, rust, dust, grit, water and any other contaminants that may get between the pad and the disc surface. One important feature is to note that our wide aperture slots also can contain significant volumes of surface gases which are created during heavy braking and prevent the pad from "aquaplaning" on these gases, allowing the pad to contact the disc better and improve brake performance.The three blind holes drilled in EBC's "GD" series are to further break down gas film in between the slots but are not "through drilled" for one very special reason. 99% of all brake rotors designed and made in the world are what we call straight vaned. This means that the ventilation slots go directly from the outer edge of the rotor, towards the centre point of the disc. There is absolutely NO BENEFIT in through drilling brake rotors which do not have the vane system designed in a "scoop" fashion (which draws air through the centre core of the disc). In fact the drilling of holes through straight vaned discs can, if the holes coincide with the positioning of the vane, weaken a disc and cause catastrophic damage.EBC Rotors are sold in pairs. So one set will cover both the left and right wheel of the front or rear of the vehicle.