ISO 2768-1 covers general tolerances for linear and angular dimensions on features where no explicit tolerance is shown: lengths, radii, chamfer heights, and angles. It defines four accuracy classes (f, m, c, v) and requires no datum references.

ISO 2768-2 is a separate standard governing geometric form tolerances — straightness, flatness, circularity, cylindricity, and run-out — using three classes (H, K, L). Both are commonly referenced together in a drawing title block, for example ISO 2768-mK, to provide full coverage for both dimensions and form. The two parts control completely different error types and are independently specified.

Class m (Medium) is the correct default for the vast majority of CNC milling and turning features. It reflects the natural accuracy envelope of modern 3-axis machine tools under standard production conditions, without requiring special fixturing, temperature control, or inspection routines.

Specifying class f for non-critical features adds cycle time, tooling qualification overhead, and inspection cost without functional benefit. For cost-sensitive parts, cross-reference tolerance selection against the DfM ebook on Xometry Pro before finalising the drawing.

This follows from basic trigonometry. The linear positional error at the end of an angle leg equals the leg length multiplied by the sine of the angular deviation. A short leg amplifies angular error into a large linear consequence at the measured surface. A long leg geometrically dilutes the same angular error.

ISO 2768-1 compensates by assigning tighter degree tolerances to shorter legs, keeping the maximum linear consequence of any angular variation within a consistent practical band.

This design produces roughly consistent linear consequence regardless of leg length, which is the practical intent of the standard.

Declare an explicit tolerance directly on the drawing for that specific feature. ISO 2768 is a catch-all baseline — it is overridden entirely by any feature-level annotation. Three main tools apply depending on the requirement:

ISO 2768-1 controls size and angular dimensions. GD&T (per ISO 1101 or ASME Y14.5) controls form, orientation, location, and run-out — the geometric relationship between features. They are complementary, not competing.

ISO 2768-2 provides a simplified substitute for GD&T form tolerances when the full datum reference framework of ISO 1101 is not warranted. Most industrial parts use a combination: ISO 2768-m(K) in the title block as the general baseline, with GD&T callouts added only on features where geometric accuracy is functionally critical.

The key rule: any explicit ISO 1101 / GD&T callout on a feature overrides the ISO 2768-2 general form tolerance for that feature, just as an explicit size tolerance overrides ISO 2768-1.

Yes. The QA Inspection mode in this calculator automates the check. Enter the nominal dimension, select the drawing class, enable QA mode, and enter the measured value. The tool returns PASS or FAIL with the deviation from the nearest limit.

Manual calculation procedure if checking without the tool:

1. Identify nominal dimension and ISO 2768 class from the drawing title block
2. Determine dimension type (linear, radius, angular)
3. Read ± tolerance from the standard table for the correct nominal range
4. Upper limit = nominal + tolerance, Lower limit = nominal – tolerance
5. Part passes if measured value falls between the two limits

Both are dimensional tolerancing standards but they apply at different levels of the same drawing and control different things.

Use ISO 2768 as the drawing baseline. Apply ISO 286 notation on any feature where fit precision directly affects assembly performance.