If a feature matters for function or fit, give it an explicit tolerance. ISO 2768-MK-E is for everything else.
1. Introduction ISO 2768-MK-E is a combined shorthand notation used on engineering drawings and technical documents. It references three parts of the ISO 2768 standard, which specifies default tolerances for linear dimensions, angular dimensions, geometrical features (form, orientation, location, and runout), and the indication of "E" for general external radius and chamfer dimensions.
– Same values as perpendicularity. Circular runout – 0.2 mm (class K). Total runout – Not defined; must be specified individually. Example: A 200 mm long machined surface without a flatness callout → allowed flatness deviation = 0.3 mm. 3.3 "E" – External Radii & Chamfer Heights (ISO 2768-1 Annex A) The "E" instructs that tolerances for external radii and chamfer heights follow the same "M" class limits as linear dimensions, but applied to the radius or chamfer size. iso 2768-mk-e
For production shops, understanding this shorthand reduces errors and clarifies expectations. For designers, using it correctly (and knowing its limits) produces clear, manufacturable drawings without over-tolerancing.
| Tolerance Class | Straightness & Flatness (mm per 100 mm) | Perpendicularity & Symmetry (mm per 100 mm) | Runout (mm) | |----------------|------------------------------------------|----------------------------------------------|--------------| | | 0.2 | 0.5 | 0.2 | If a feature matters for function or fit,
| Nominal Range (mm) | Straightness / Flatness (± mm) | Perpendicularity (± mm) | |--------------------|--------------------------------|-------------------------| | ≤10 | 0.05 | 0.1 | | >10 to 30 | 0.1 | 0.2 | | >30 to 100 | 0.2 | 0.3 | | >100 to 300 | 0.3 | 0.4 | | >300 to 1000 | 0.4 | 0.5 | | >1000 to 3000 | 0.5 | 0.6 |
| Part | Title | Purpose | |------|-------|---------| | | General tolerances for linear and angular dimensions | Defines tolerance classes (f, m, c, v) for sizes, radii, chamfers, and angles | | ISO 2768-2 | General tolerances for geometrical features | Defines tolerance classes (H, K, L) for straightness, flatness, parallelism, perpendicularity, symmetry, runout | Introduction ISO 2768-MK-E is a combined shorthand notation
| Feature Type | Rule | |--------------|------| | Length, width, height | ± mm from "M" linear table | | Hole diameter | Not covered (size tolerance must be given individually unless it's a general dimension) | | Hole position | Covered by "K" position tolerance (0.5 mm per 100 mm) | | Flatness of a surface | 0.2 mm per 100 mm (class K) | | Perpendicularity of a shoulder | 0.5 mm per 100 mm (class K) | | External fillet radius R5 | ±1.0 mm (since 5 mm is in >3–6 range, "E") | | Chamfer C2 | ±0.5 mm (from "E" table) |