The one piece design is far superior to common bolt together two piece rotors in weight reduction, strength, and longevity. All Strange Pro Race Rotors are slotted. Every kit includes 4-piston directional caliper. The directional caliper accomplishes superior bridge bolt strength at only 2.70 pounds. Strange directional calipers feature 1.750" and 1.625" OD stainless steel pistons to assure optimal pad wear and exceptional / handle feel. Every Strange caliper is internally ported and include .100" square o-rings to assist piston retracton.