A block gauge is a rectangular-shaped gauge used as a length standard. It is made of a hard material that does not change with time, and is finished so that two of the six faces of a pair of rectangles are flat and parallel to an extremely high standard, and the distance between the two faces is the correct specified dimension. A number of blocks of different lengths are supplied as a set, and are used either individually or in pairs by sticking them together (so-called "linking").
Terminology