A go-no-go gauge can also be used for adjusting the valves on an engine. It eliminates the "feel" of what the gap should be. If the valve adjustment you are trying to achieve is .003 of an inch then you would use a .002 (go) and .004 (no-go) and that gives you .003 valve lash. The feeler gauge has the .002 and the .004 built into the same blade.