Starrett 690M-2Z Hole Gauge Dial Bore Gauge, 0.75-3.30mm Range, 0.02mm Graduation

The Starrett 690M-2Z Hole Gauge Dial Bore Gauge has a measurement range of 0.75 to 3.30 mm and gradient spacing of 0.02 mm. The gauge can be pressed down on a flat surface and checked so the size reads the same as the set number stamped on the back of the indicator. The balanced design makes for easy one-handed operation and all ground surfaces are made of hardened tool steel for durability.

Bore gauges measure holes, or bores, in a workpiece. They can measure the interior diameter of a hole at any depth, while internal micrometers can only measure to the depth of their teeth. Bore gauges are typically calibrated with a setting ring and come in two types: simple and direct-measuring. Simple bore gauges are used with a caliper to transfer the hole measurement, while the more complex gauges take the measurement directly, and display it through a vernier, dial, or digital display. Bore gauges have a two- or three-point contact, indicating how many points on the gauge head touch the inside of the bore. Two-point contacts are better at measuring ovality, while three-point contacts are used to measure lobing or triangular form error. Pistol-grip bore gauges are used for fast, single-handed operation with repeatable results from one operator to another. Bore gauges can also be used in special applications, such as measuring threads, spline pitch diameters, and deep bores.

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.