Limitations:
Instead of detailing a unique ± value for hundreds of non-critical dimensions, designers can write a single note in the drawing title block: "General tolerances according to ISO 2768-mh" . This makes the drawing clean and easy to read.
(Form and position tolerances should be specified per ISO 2768‑2 or better, per ISO 1101.)
The "h" class defines the general tolerances for geometric characteristics. : Up to 10 mm: 0.1 mm 10 to 30 mm: 0.2 mm 30 to 100 mm: 0.4 mm 100 to 300 mm: 0.8 mm 300 to 1000 mm: 1.2 mm
"The 'H' means the same as the 'm'." Reality: No. 'H' is specifically from ISO 2768-2. It defines geometry, not size. A part can be the wrong size (within 'm') but perfectly flat (within 'H'). iso 2768-mh tolerance chart
These tolerances control orientation but not form deviations .
The answer is cost. Tight tolerances require grinding, lapping, and CMM inspection. If a 100mm long cosmetic cover plate is dimensioned at 100mm ±0.01mm because the drafter forgot to set defaults, the part will cost 500% more than necessary.
Angular dimensions apply to the general feature orientation. Length of Shorter Leg (mm) Tolerance m (Medium) Above 10 up to 50 ±30' (0.5°) Above 50 up to 120 ±20' (0.33°) Above 120 up to 400 ±10' (0.16°) ±5' (0.08°) 3. ISO 2768-2 Geometrical Tolerances (H)
ISO 2768 is an international standard aimed at simplifying technical drawings by defining general tolerances for linear and angular dimensions, as well as geometrical tolerances (straightness, flatness, etc.). It is divided into two main parts: Limitations: Instead of detailing a unique ± value
The ISO 2768-2 standard provides general geometrical tolerances for features that do not have individual tolerance indications. The "H" (High) class is more restrictive than "K" or "L". A. General Tolerances for Straightness and Flatness Up to 10mm: Over 10 to 30mm: Over 30 to 100mm: Over 100 to 300mm: Over 300 to 1000mm: Over 1000 to 3000mm: B. General Tolerances for Perpendicularity Up to 100mm: Over 100 to 300mm: Over 300 to 1000mm: Over 1000 to 3000mm: C. General Tolerances for Symmetry Up to 100mm: Over 100 to 300mm: Over 300 to 1000mm: Over 1000 to 3000mm: D. General Tolerances for Circular Run-out All diameters: (for "H" Class) How to Properly Apply ISO 2768-mH
While this is a valid and common standard, be aware that you can have a linear dimension that passes inspection (it falls within ±0.2mm), but the part can still fail functionally because the flatness or perpendicularity is off by a larger margin allowed by the "H" class.
ISO 2768 is a standard providing general tolerances for linear and angular dimensions on technical drawings when no specific tolerance is indicated. This paper explains the scope and purpose of ISO 2768, details the tolerance classes (f, m, c, v), focuses on the “m” (medium) grade for machining (ISO 2768‑m), discusses the interpretation and application of ISO 2768‑m for linear, angular, and geometric features, shows worked examples and charts, comments on limitations and best practices, and compares ISO 2768 with other tolerance systems. Practical recommendations and a sample tolerance chart for ISO 2768‑m are included.
Next time you see that title block, you’ll know exactly what margin of error the shop floor is working with. : Up to 10 mm: 0
| Nominal Size Range (mm) | Tolerance (mm) | |------------------------|----------------| | 0.5 up to 3 | ±0.1 | | >3 up to 6 | ±0.1 | | >6 up to 30 | ±0.2 | | >30 up to 120 | ±0.3 | | >120 up to 400 | ±0.5 | | >400 up to 1000 | ±0.8 | | >1000 up to 2000 | ±1.2 | | >2000 up to 4000 | ±2.0 |
| Dimension Range for Radii/Chamfer (mm) | Tolerance Class 'm' (mm) | | :--- | :--- | | 0.5 up to 3 | ±0.2 | | >3 up to 6 | ±0.5 | | >6 up to 30 | ±1.0 |
To appreciate the 'm' and 'H', compare them to other classes.