ISO 2768

In practice

Class m allows ±0.2 mm on dimensions over 6 mm up to 30 mm. Part 2, which covered geometric tolerances in classes H, K, and L, was withdrawn in favor of ISO 22081 but still appears on many drawings.

Related terms

Tolerance

Tolerance is the total amount a dimension is allowed to vary from its nominal value, such as ±0.005 in (±0.13 mm). Tighter tolerances raise cost through slower processes, extra operations, and added inspection. Hold them only on features that affect fit or function.

GD&T

GD&T is geometric dimensioning and tolerancing, the symbol system defined in ASME Y14.5 and ISO 1101 for controlling the form, orientation, location, and runout of part features relative to datums. It states functional intent more precisely than plus-minus dimensions and often allows larger tolerances where they do not matter.

2D drawing

A 2D drawing is a dimensioned engineering drawing, usually a PDF, that defines a part's tolerances, datums, material, finish, and inspection requirements. The 3D model shows shape; the drawing controls what gets measured and accepted. Most quality agreements make the drawing the governing document when the two disagree.