Basic hole

A basic hole is one of the systems of Fit employed in Mechanical engineering. It is used to avoid large numbers of tolerances. In the case of a basic hole, the hole in a fit is manufactured in a standardised process, while the corresponding Tolerance is transferred to the Shaft.

This means always using the same tool to machine certain holes in workpieces, so that the diameter of the hole (e.g. on shaft-Hub joints) is always the same size. The Drilling tool will have two or more Cutting edges that do not permit geometric adjustment. By contrast, the diameter of the corresponding shaft is machined (usually turned) to be smaller or larger so as to produce the desired fit (e.g. press fit, clearance fit).

Due to low tool costs, the basic hole process is cheap and therefore commonplace.