The valve tappet clearance gauge checks the minimum (.028”) and maximum (.080”) clearance gap between the rocker arm and the valve stem cap when the lifter (tappet) is dry and fully collapsed. The blades are ground and polished to precisely .080” and .028” for Lycoming Engines. This gauge does the same job as the comparable Lycoming product that sells for well over $150, and is a must to make sure your engine is firing correctly.