Steel Rule Depth Gage is very handy and can be used to quickly obtain measurements in 64th of an inch or 1/2mm by simply adjusting the rule to the required depth. FEATURES: Gage consists of a nicely finished, hardened steelhead and an accurate, machine divided, tempered steel rule. Rules are either 610N (6 inches) or 635N (150mm) models. Gage can be smoothly adjusted to the required measurement and then locked into position by a knurled nut. The base is cut out on one side, adjacent to the rule, permitting easier readings and more accurate measurements. 6" hook rule also available, permitting easier readings from the edge of a workplace to the edges of the slots, and shoulders.