The older style 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.