Wide aperture grooves. Special disc alloys UNIQUE to EBC. Dimple hole construction. Balanced geometry. The wider slot actually draws cool air across the pad surface keeping pads and rotors cooler. They also expel dust, dirt and hot gases better than fine slots which eventually fill with rust and scale and become ineffective in our opinion. The blind drilled holes break down surface gases when braking from speed but do not weaken the rotor cross section as can happen with through drilling, thereby lessening the chance of rotors cracking over time and heavy use. All EBC Discs are supplied as pairs.