Pit Stop USA is The Online Motorsports Superstore! MAHLE, manufacturer of Perfect CircleA piston rings, is the largest manufacturer of piston rings in the world, leads the way in ring technology and innovation. Perfect Circle rings are at the forefront of both light and heavy vehicle piston ring technology. Extensive OE connections mean that Perfect Circle rings have the technological edge. Things like the CP-20 oil ring, narrow compression rings, steel compression rings for gasoline engines, low tension oil rings and coated compression rings for diesels all came from the OE. Now, MAHLEas rededication to the Perfect Circle performance line proves that Perfect Circle should be the ring choice under every hood - regardless of the application. Until recently, grey cast iron or ductile iron was the material of choice for automotive applications - today, steel is preferred over iron by more and more engine designers. Steel compression ring technology, pioneered by the former Perfect Circle group, has been used in heavy-duty applications for over 30 years. That know how has become essential to the design and engineering of today's automotive engines. Steel piston rings offer higher tensile strength, higher yield strength, greater fatigue life, and greater hardness while still offering a lower ring mass. These factors lead to better stress resistance, reduced groove pound-out, longer service life, better conformability, superior oil economy, and superior blow-by control while still lowering friction. Whether you're repairing a modern computer controlled engine, or rebuilding an older engine, be sure to specify Perfect Circle piston rings - trusted by professional automotive technicians for over 100 years. We feature Perfect CircleA Plasma-Moly File Fit Piston Ring Sets at low everyday prices!