The old standard shims will not hold up to the extreme spring pressures and high RPM found in racing engines being built today. COMP Cams® offers a simple but effective solution to this problem − a thin, hardened steel alloy seat which will not only protect the head and shim, but also locate and hold the spring in place. Previously, this part has been available only in a cup form with the retaining portion being on the outside of the part. This required that the head be machined a great deal to accept this cup so COMP® now offers an I.D. locator with the locating shoulder on the inside, as well as the spring cup. Many sizes are available to locate from the inside or outside diameter