A gauge 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 a hardened steel alloy, while calibration grade blocks are often made of tungsten carbide or chromium carbide because it is harder and wears less. Gauge blocks come in sets of blocks of various lengths, to allow a wide variety of standard lengths to be made up by stacking them. The length of each block is actually slightly shorter than the nominal length stamped on it, because the stamped length includes the lengthof one wring film, a film of lubricant which separates adjacentblock faces in normal use. In use, the blocks are removed from the set, cleaned of their protective coating to form a stack of the required dimension, with the minimum number of blocks. Gauge blocks are calibrated to be accurate at 68 Degree F (20 Degree C) and should be kept at this temperature when taking measurements. This mitigatesthe effects of thermal expansion. Gauge blocks (also known as gage blocks, Johansson gauges, slip gauges are a system for producing precision lengths. The individual gauge block is a metal or ceramic block that has been precision ground and lapped to a specific thickness. Gauge blocks come in sets of blocks with a rangeof standard lengths. In use, the blocks are stacked to make up a desired length. An important feature of gauge blocks is that they can be joined together with very little dimensional uncertainty. The blocks are joined by a sliding process called wringing, which causes their ultra flat surfaces to cling together. A small number of gauge blocks can be used to create accurate lengths within a wide range. By using 3 blocks from a set of 30 blocks, one may create any of the 1000 lengths from 3.000 to 3.999 mm in 0.001 mm steps.