Gage block calibration is one of the oldest high precision calibrations made in dimensional metrology. Gage blocks are the main means of length standardization used by the industry today. A gage block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart. Standard grade blocks are made of steel; while calibration grade blocks are tungsten carbide and have the advantage of being harder and longer wearing than steel.
Gage blocks come in a variety of lengths and numbers in a given set. Gage blocks are also available in various grades, depending on their intended use. The grade of the gage block is determined by the tightness of the tolerance applied to the gage block. Thus higher-grade blocks are made to tighter tolerances and have higher accuracy and precision.
Gage blocks should only be used for calibration of other tools (i.e. calipers, micrometers, special fixtures) they should not be used with machinery that would mar, scrape or apply excessive pressure to the block. If the gage block becomes worn or damaged it must be replaced, it cannot be reworked. To keep the gage block clean, use a soft cloth and mineral spirits before and after each use. The measuring surface of the gage block should never be touched with bare fingers (acids and other contaminants can corrode steel blocks). Industry consensus is that gage blocks should be calibrated every 1 to 3 years. The customer can determine the tolerance to apply to the gage block set (down grading is possible as long as the set meets the customers’ needs).
Gage blocks are essentially the building blocks of measurements and should be treated as such. Keeping up with the care and calibration of a gage block set will be worth the investment because there will be no need for replacement – the technology remains the same. Gage blocks are an original concept.