When you specify , you are assuming standard machining precision.
The standard is split into two distinct parts, represented by the two letters. Misunderstanding which letter applies to which dimension is the most common source of quality errors. iso 2768 m k
Permissible deviations (±) in millimeters based on the nominal size of the feature: Nominal Length Range (mm) Tolerance (± mm) Over 3 to 6 Over 6 to 30 Over 30 to 120 Over 120 to 400 Over 400 to 1,000 Over 1,000 to 2,000 Over 2,000 to 4,000 Angular Dimensions (Class m) When you specify , you are assuming standard
is the workhorse of the mechanical engineering world. It is the "Goldilocks" setting—neither too tight (expensive) nor too loose (sloppy). Permissible deviations (±) in millimeters based on the
Ask any CNC operator about "mK," and they will likely sigh with relief. Here is why:
ISO 2768-mK is a safety net, not a straitjacket. If a critical hole requires a tolerance of H7 (±0.015mm), you must call that out directly on the dimension. The general "mK" tolerance applies only to dimensions without individual tolerance annotations.
Could you please clarify which part of the standard you are interested in or if you need a general overview of both?