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Gage Blocks

Gage blocks (also called gauge blocks, Jo blocks, Hoke blocks, and Johansson gauges) are precision ground and lapped metal or ceramic blocks, used for calibrating precision measuring equipment and as a length standard in manufacturing. Gage blocks are square or… Learn More

Gage blocks should be kept within a protective case, cleaned thoroughly before wringing and after each use to prevent corrosion, and kept free of burrs and other damage that would decrease their accuracy. Temperature is another important consideration. Blocks are susceptible to thermal expansion and must be used at room temperature (68 degrees F) to ensure their accuracy.

Gage blocks are available in different grades, which refer to their tolerance or allowable deviation from their nominal dimension. Grades are defined by the American Society of Mechanical Engineers (ASME) B89.1.9M for both length and flatness. ASME B89.1.9M also defines standards for parallelism and surface finish. Different grades are available depending on the application and the required level of accuracy. Grade 00 blocks are generally used to calibrate and check the accuracy of instruments, grade 0 blocks for setting and checking gages in quality control, grade AS-1 blocks for tool rooms and production purposes, and grade AS-2 are similar to AS-1 blocks but are slightly less accurate. Grade K blocks are used for calibrating and checking the accuracy of other gage blocks within a temperature-controlled inspection or calibration room. A certificate of inspection and calibration is provided with each gage block or set, specifying the deviation of the individual block from its nominal length.

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