The Starrett 640 Series Dial Depth Gauges, Indicator Type, Inch, have a measurement range of 0 to 0.5", a resolution (or smallest graduation interval) of 0.0005", with + or - 1 graduation (0.0005") for the first 2.5 revolutions of accuracy. The dial face has distinct, easy to read figures. The 640JZ model has a simple one-button design to take accurate measurements. The 640RJZ model has reverse movement (no button) and can be operated with one hand for ease of use. The gauges in this series have hardened and ground bases that are 2.5" long and are used as a reference for measurements. These gauges come in a fitted case. Electronic indicators are sold separately. Depth gauges are typically used in manufacturing, machining, and mechanical engineering.
Depth gauges are precision measuring instruments used to determine the depth of any shape that has a step, groove, or slot. These gauges often take the form of sliders that travel on a measuring beam or rods, are moved to position by hand, and then adjusted with a calibrated screw. The base of the gauge rests at the top of the shape whose recession is to be measured, while the beam or rods extend to the bottom of the recession to determine the measurement. Gauge position is read from a graduated scale, dial, counters, or an electronic display.
The L.S. Starrett Company manufactures precision measuring tools, metrology and testing equipment, and saw blade products. The company, founded in 1880, is headquartered in Athol, MA.