Glossary
ISO 2768 — definition
The standard for general tolerances on machined dimensions that carry no individual tolerance on the drawing.
A drawing cannot give every single dimension its own tolerance. ISO 2768 solves that by stating one general class covering everything not specified individually.
The classes for linear dimensions are f (fine), m (medium), c (coarse) and v (very coarse). A second letter — H, K or L — sets tolerances for form and position.
A common and expensive mistake is writing the finest class in the title block “just to be safe”. That makes the whole part more expensive to machine and to inspect, with no functional gain.
The right approach is to set a generous general class and specify tight tolerances explicitly on the five or six dimensions that actually determine the function.