ISO 2768 governs every dimension on a drawing that has no individual tolerance. A title-block note such as ISO 2768-mK assigns class m to all unmarked linear and angular dimensions (ISO 2768-1) and class K to all unmarked straightness, flatness, perpendicularity, symmetry and run-out (ISO 2768-2). Every value of both parts is below, in real HTML tables.
Compiled and reviewed by the EKINSUN engineering team — a custom parts manufacturer machining to these classes daily. Values per ISO 2768-1:1989 and ISO 2768-2:1989 (DIN ISO 2768 identical). Last reviewed 18 Aug 2026.
The note is always lowercase linear class + capital geometric class. The linear letter comes from ISO 2768-1 — f (fine), m (medium), c (coarse), v (very coarse). The geometric letter comes from ISO 2768-2 — H, K or L, H being tightest. The two letters are independent choices:
| Drawing note | Linear class | Geometric class | Typical use |
|---|---|---|---|
| ISO 2768-mK | m — medium | K — medium | The default of general machining. Most drawings we quote carry this note |
| ISO 2768-fH | f — fine | H — tight | Machined parts with several mating faces; halves the m allowances without per-feature callouts |
| ISO 2768-cL | c — coarse | L — loose | Welded frames, flame-cut and sawn parts — not finish machining |
| ISO 2768-m (one letter) | m — medium | none invoked | Only Part 1 applies; geometry is uncontrolled unless drawn |
Permissible deviations in mm for unmarked linear dimensions: lengths, widths, diameters, steps, distances. Below 0.5 mm the standard gives no general tolerance — those dimensions must be individually stated on the drawing.
| Nominal range | f (fine) | m (medium) | c (coarse) | v (very coarse) |
|---|---|---|---|---|
| 0.5 – 3 | ±0.05 | ±0.1 | ±0.2 | — |
| >3 – 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 |
| >6 – 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 |
| >30 – 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 |
| >120 – 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 |
| >400 – 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 |
| >1000 – 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 |
| >2000 – 4000 | — | ±2.0 | ±4.0 | ±8.0 |
Worked example: a shaft drawn as plain "Ø20 × 85" under ISO 2768-mK may measure Ø19.8–20.2 and 84.7–85.3 mm and is in specification. If that Ø20 is a bearing seat, general tolerance is the wrong tool — it needs an ISO 286 fit callout such as 20 k6.
Broken edges, chamfer heights and external radii get much wider allowances than linear dimensions — by design, because nobody should pay precision money for a deburring chamfer:
| Nominal range | f | m | c | v |
|---|---|---|---|---|
| 0.5 – 3 | ±0.2 | ±0.2 | ±0.4 | ±0.4 |
| >3 – 6 | ±0.5 | ±0.5 | ±1.0 | ±1.0 |
| >6 | ±1.0 | ±1.0 | ±2.0 | ±2.0 |
Angular allowances are stated in degrees and minutes and shrink as the shorter leg of the angle gets longer — a long face amplifies the same angular error into more millimetres at its end:
| Shorter side | f | m | c | v |
|---|---|---|---|---|
| ≤ 10 | ±1° | ±1° | ±1°30′ | ±3° |
| >10 – 50 | ±0°30′ | ±0°30′ | ±1° | ±2° |
| >50 – 120 | ±0°20′ | ±0°20′ | ±0°30′ | ±1° |
| >120 – 400 | ±0°10′ | ±0°10′ | ±0°15′ | ±0°30′ |
| >400 | ±0°5′ | ±0°5′ | ±0°10′ | ±0°20′ |
Part 2 sets general limits for form and orientation where the drawing has no GD&T frame. It covers straightness, flatness, perpendicularity, symmetry and circular run-out — and nothing else. Position, concentricity, cylindricity and profile are not in the standard and stay uncontrolled unless drawn.
| Nominal range | H | K | L |
|---|---|---|---|
| ≤ 10 | 0.02 | 0.05 | 0.1 |
| >10 – 30 | 0.05 | 0.1 | 0.2 |
| >30 – 100 | 0.1 | 0.2 | 0.4 |
| >100 – 300 | 0.2 | 0.4 | 0.8 |
| >300 – 1000 | 0.3 | 0.6 | 1.2 |
| >1000 – 3000 | 0.4 | 0.8 | 1.6 |
| Nominal range | H | K | L |
|---|---|---|---|
| ≤ 100 | 0.2 | 0.4 | 0.6 |
| >100 – 300 | 0.3 | 0.6 | 1.0 |
| >300 – 1000 | 0.4 | 0.8 | 1.5 |
| >1000 – 3000 | 0.5 | 1.0 | 2.0 |
| Nominal range | H | K | L |
|---|---|---|---|
| ≤ 100 | 0.5 | 0.6 | 0.6 |
| >100 – 300 | 0.5 | 0.6 | 1.0 |
| >300 – 1000 | 0.5 | 0.8 | 1.5 |
| >1000 – 3000 | 0.5 | 1.0 | 2.0 |
| Feature | H | K | L |
|---|---|---|---|
| Circular run-out (any size) | 0.1 | 0.2 | 0.5 |
EKINSUN LTD is a custom parts manufacturer in Guangdong, China, and machines unmarked dimensions to ISO 2768-mK by default. The default is written on the quotation, so it is agreed — not assumed — before metal is cut. Where a sketch or a sample replaces a drawing entirely (we accept both), the quote states the class we will hold, and any feature you call out gets its own tolerance:
| Tolerance level | Typical callout | Cost effect | How it is verified |
|---|---|---|---|
| General machining | ISO 2768-mK (our default) | None — included in every quote | Calipers / micrometer sampling |
| Fine general | ISO 2768-fH | Small step | Micrometer + surface plate checks |
| Feature tolerance | ±0.05 mm on stated features | Priced per feature, not per part | In-process gauging |
| Precision feature | ±0.02 / ±0.01 mm, ISO 286 fits | Meaningful — only where it works | CMM report on request |
Material behaviour is part of holding these classes: 6061 and 7075 aluminium machine stable and hold m-class flatness easily; 304 and 316 stainless work-harden and spring, so long thin stainless parts get stress-relief and lighter finishing passes to stay inside the same table; brass is the most forgiving of all. ISO 2768 values are defined at 20 °C — on anodised parts we also state whether dimensions apply before or after coating, because anodising grows each surface by up to 0.025 mm and a general-tolerance part can walk out of spec in the tank.
| Situation | Covered by ISO 2768? | How EKINSUN handles it |
|---|---|---|
| Unmarked lengths, diameters, steps on a machined part | Yes — class m/f per the tables above | Machined to 2768-mK by default, class stated on the quote |
| A bearing seat, bushing bore or press fit | No — ±0.2 mm is ~20× an H7 zone | ISO 286 callout; both halves of the fit cut to the limits & fits chart |
| A bolt-hole pattern that must line up with a mating part | No — Part 2 has no position tolerance | Explicit position callout, or we machine both mating parts so the pattern is cut once |
| Threads | No — threads carry 6g/6H classes | Thread gauged to its own class; non-standard threads machined to order |
| Dimensions under 0.5 mm | No general tolerance exists there | Individually toleranced on the drawing, or we propose the value on the quote |
| Surface texture | No — Ra is a separate specification | Ra stated per the surface roughness chart, matched to the class of fit |
| A worn sample with no drawing at all | 2768 presumes a nominal to deviate from | Reverse engineering recovers nominals first, then the class is applied |
Drawing says 2768-mK — or says nothing at all? Send the drawing, sketch or sample. We quote in 12 hours with the tolerance class stated, machine to it from 1 piece, and tighten single features to ±0.01 mm where the function needs it. Get a quote.
The lowercase letter is the ISO 2768-1 linear class, the capital is the ISO 2768-2 geometric class. ISO 2768-mK puts every unmarked linear and angular dimension in class m (a 6–30 mm dimension carries ±0.2 mm) and every unmarked flatness, straightness, perpendicularity, symmetry and run-out in class K.
Strictly, none — the note is incomplete without a class letter. In practice most shops read bare ISO 2768 as 2768-mK, the most common combination. EKINSUN quotes such drawings as 2768-mK and states that assumption on the quotation so it can be corrected before machining.
Unmarked dimensions are machined to ISO 2768-mK by default: ±0.1 mm on a 3–6 mm feature, ±0.2 mm on 6–30 mm, ±0.3 mm on 30–120 mm. The default is stated on the quotation, and any single feature can be tightened to ±0.05 mm or ±0.01 mm on request without re-pricing the whole part.
No. ISO 2768-m allows ±0.2 mm at 6–30 mm, roughly 20 times wider than the 21 µm zone an H7 bearing bore needs at Ø25. Fits must carry an ISO 286 callout such as 25 H7 or 25 g6 — EKINSUN machines both halves of the fit to the ISO 286 chart, not to general tolerances.
Class fH halves the linear allowance (±0.1 mm instead of ±0.2 mm at 6–30 mm) and roughly halves the geometric allowances. Specify fH when the part has several mating faces or located features and you want them all held tighter without tolerancing each one individually. CNC-machined parts reach fH without special processes, so the cost step is small — far smaller than tolerancing every dimension at ±0.05 mm.
No. Threads carry their own tolerance classes — 6g for external, 6H for internal metric threads by default — and are unaffected by the general-tolerance note. ISO 2768 also excludes dimensions below 0.5 mm and anything already carrying an individual tolerance or a GD&T frame.
No — ISO 2768-2 covers straightness, flatness, perpendicularity, symmetry and run-out, but has no position tolerance. A bolt-hole pattern controlled only by general tolerances is controlled only through its coordinate dimensions, so patterns that must line up with a mating part need an explicit position callout.
Yes. General tolerance classes are the floor, not the ceiling: selected features are routinely machined to ±0.05 mm, ±0.02 mm or ±0.01 mm with in-process gauging and a CMM dimensional report. State the tight tolerance only on the features that need it and leave the rest on 2768-mK — that is the cheapest way to a precise part, MOQ 1.
Drawing, sketch or sample — machined to ISO 2768-mK, fH, or tighter per-feature tolerances. MOQ 1, quote in 12 hours.
Custom machined parts held to ISO 2768-mK, fH or tighter — from a drawing, sketch or worn sample. MOQ 1, quote in 12 hours.