Gauge block is a precision ground (and lapped) length measuring standard. They are used as a reference for the calibration of precision measuring equipment used in machine shops, such as micrometers, sine bars, calipers, and dial indicators (tools used in an inspection role) and are still the main means of length standardization used by the industry today.



Gauge blocks come in sets of blocks of various lengths, along with two wear blocks, to allow a wide variety of standard lengths to be made up by stacking them. Each gauge block is essentially 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 a hardened steel alloy, while our calibration grade blocks are often made of tungsten carbide, a tougher alloy which renders these blocks harder and more resistant to wear and tear overtime.

In use, select blocks are removed from the set, cleaned of their protective coating (petroleum jelly or oil) and wrung(1) together, advisably, using the minimum number of blocks to form a stack of the required dimension.

‘Wear blocks’, made of a harder substance like tungsten carbide, are included at each end of the stack whenever possible, to protect the actual gauge blocks from being damaged or worn down when in use.

Note that gauge blocks are calibrated to be at their most accurate at approximately 20 °C and should be kept at this temperature when taking measurements. This mitigates the effects of thermal expansion. Also, the length of each block is actually slightly (microns) shorter than the nominal length stamped on it, because the stamped length includes the length of one wring film, a film of lubricant which separates adjacent block faces in normal use.


Wringing is the process of sliding two blocks together so that their faces lightly bond

The process of wringing involves four steps:

1: Wiping a clean gauge block across an oiled pad.
2: Wiping any extra oil off the gauge block using a dry pad.
3: The block is then slid perpendicularly across the other block while applying moderate pressure until they form a cruciform.
4: Finally, the block is rotated until it is in line with the other block.

After use, the blocks are once again oiled or greased to protect against corrosion.

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