Blade type anvil and spindle for measuring circular form tools, diameter, and depth of narrow grooves, slots, keyways, recesses, shallow depths, between lands and fins. Non-rotating spindle prevents blade turning. Blades .030" thick, measure depths to 5/16". Speeder on the end of thimble for faster settings and measurements. Specially forged, black enameled frame with satin chrome finish on sleeve and thimble.