Federal-Mogul designs and engineers pistons to meet the most demanding street performance and racing conditions. In combination, we draw upon more than 100 years of Federal-Mogul engine mastery to enhance the piston ring and its seal. Our Speed-Pro® brand is recognized for being a winner in every form of racing, and is the proven horsepower leader in oval track and drag racing. Hell Fire® Rings: Speed-Pro Hell Fire rings, manufactured from a specially hardened and tempered ductile iron alloy, are engineered to thrive in extreme racing conditions. These rings retain tension under the most brutal operating conditions, including engines that rely on megadoses of nitrous oxide. Proven in Pro Street, IHRA Pro-Mod and NHRA Top Fuel & Funny Car racing, Hell Fire rings will not flake, and the SS-50 oil rings keep chambers dry, preventing detonation. Pro Series Rings: Speed-Pro Pro Series rings, designed for the professional racer, offer features that maximize horsepower, including: Reduced widths and radial wall thicknesses in the top and second rings for lower tension and enhanced sealing - Plasma-moly facing on the top ring for instant seating and long life - Cast iron second rings, with tapering face profile and open-gap design for lower inter-ring pressure buildup and excellent oil control at even the highest RPMs - Pro Series rings include a very low-tension, thin-profile version of the SS-50 oil rings with a wire latch mechanism to simplify installation.Pit Stop USA offers Speed-Pro File Fit Plasma Moly Piston Ring Set - 4.000" Bore (+.035") - Top Ring: 1/16", 2nd Ring: 1/16", Oil Ring: 3/16", Oil Tension Ring: Low R9401-35 at low everyday prices. Be sure to check out all of our products from Speed Pro including Speed Pro Speed-Pro File-Fit Plasma Moly Piston Rings.