COMP Cams® offers a complete line of valve stem seals, from the stock GM O-Ring to the positive-stop Teflon® seal. These seals are a must to keep unwanted oil from entering the combustion chamber through the clearance in the valve guides. The O-Ring seals use the standard retainer and oil splash shield. The umbrella seal is normally used when a larger-than-stock diameter spring is used, in the case of a double spring, the positive-stop Teflon® seal is used. We also have a smaller diameter Viton seal available for triple spring applications. Both the O-Ring and the umbrella seals require no machining, but with the Teflon® seal it is necessary to disassemble the heads and machine the top of the guide with a special . 530 diameter cutter. Whenever you are planning an engine overhaul or a cam change, don't forget the valve seals. For 4 Cylinder use -8 suffix, for 6 Cylinder use -12 suffix.Pit Stop USA offers Comp Cams Valve Seals - Positive Stop Teflon - .530" Guide - 5/16" - (Set of 16) 500-16 at low everyday prices. Be sure to check out all of our products from Comp Cams including Comp Cams Valve Stem Seals.