Iso 2768-mh Tolerance Chart

You might ask: Why not just tolerance every single hole and edge?

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.

ISO 2768-mH provides a safety net:

Below is a practical reproduction of the ISO 2768‑1 linear tolerance values for grade "m" (medium). Note: the exact numbers below are representative; always verify against the official ISO 2768‑1:1989/2000 standard edition used by your organization or the most current national adoption.

Tolerance (grade m) for length L (mm):

(Explanation: For a nominal dimension within each size range, the permissible deviation is ± the listed value.)

Angular tolerances (when not otherwise specified), typical values for grade m:

Notes:

| Nominal Dimension Range (mm) | Permitted Deviation (± 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 | iso 2768-mh tolerance chart

✅ Example: A 50 mm width without a specific tolerance is allowed to be 50 mm ±0.3 mm.

ISO 2768 defines tolerance grades for linear dimensions:

Each grade is applied to ranges of nominal sizes. The tolerance for a dimension equals the tolerance value from the chart corresponding to the nominal size and selected grade. The “m” grade gives moderate tolerances suitable for general machining.

ISO 2768‑1 also provides default angular tolerances (e.g., ±1° for coarse grades, ±0.5° for medium — see the standard for exact figures) and for unspecified radii/chamfers. You might ask: Why not just tolerance every

ISO 2768‑2 provides default values for geometrical tolerances when such symbols are omitted, but it is safer to specify geometric controls directly when required.

| Nominal Length Range (mm) | Tolerance (mm) | |--------------------------|----------------| | ≤ 10 | 0.02 | | >10 to 30 | 0.05 | | >30 to 100 | 0.1 | | >100 to 300 | 0.2 | | >300 to 1000 | 0.3 | | >1000 to 3000 | 0.4 |

| Nominal Hole Size (mm) | Tolerance Grade (implied) | Tolerance (± or +/–) | |------------------------|---------------------------|----------------------| | ≤3 | IT13 | +0.14 / 0 | | >3–6 | IT13 | +0.18 / 0 | | >6–10 | IT13 | +0.22 / 0 | | >10–18 | IT13 | +0.27 / 0 | | >18–30 | IT13 | +0.33 / 0 | | >30–50 | IT13 | +0.39 / 0 | | >50–80 | IT13 | +0.46 / 0 | | >80–120 | IT13 | +0.54 / 0 | | >120–180 | IT13 | +0.63 / 0 | | >180–250 | IT13 | +0.72 / 0 | | >250–315 | IT13 | +0.81 / 0 |

✅ Example: A 20 mm diameter hole with no tolerance is allowed to be 20.00 mm to 20.33 mm. It can never be 19.98 mm. (Explanation: For a nominal dimension within each size

⚠️ Important: H means only positive deviation (hole gets larger). This ensures assembly with shafts, pins, or bolts.