The standard ISO DIN 2768 is a standard has been issued by the International Organization for standardization - ISO in association with Deutsches Institut für Normung - DIN. This standard determines the general tolerance values for the untoleranced linear and angular dimensions and also for the form and position tolerances. It's used to simplify the engineering drawings in case of determining the mechanical tolerances for parts' dimensions which are manufactured by machining means.
This standard consists of two sub-standards:
1- ISO DIN 2768-1 Standard:
This sub-standard determines the values of general tolerances of the linear and angular dimensions and radius of curvature and chamfer height according to four classes of levels: f (fine), m (medium), c (coarse), v (very coarse).
2- ISO DIN 2768-2 Standard:
This sub-standard the values of general tolerances in regard of form and posistion according to three classes or levels: H (fine), K (medium), L (coarse).
In engineering drawings, and for the untoleranced dimensions, the medium level is usually used ( "m" for the first sub-standard and "k" for the second sub-standard), and that can be expressed by writing the following in the title box: ISO DIN 2768 - mK.