ISO 286 Fit & Tolerances Chart
Reference tables for ISO 286 fits and tolerances: IT grades by nominal size, clearance–transition–interference categories, and hole-basis / shaft-basis preferred combinations—H7/g6, H7/h6, H7/p6, and the rest of the shop standards.
Standard Tolerance Grades (IT)
International Tolerance (IT) values in micrometres by nominal size step. Combine a fundamental deviation letter with an IT number to form a tolerance class—H7, g6, k6, p6, and so on.
| Nominal range (mm) | IT4 | IT5 | IT6 | IT7 | IT8 | IT9 | IT10 | IT11 |
|---|---|---|---|---|---|---|---|---|
| Over 0 – 3 | 2 | 3 | 4 | 6 | 10 | 14 | 25 | 40 |
| Over 3 – 6 | 2.5 | 4 | 5 | 8 | 12 | 18 | 30 | 48 |
| Over 6 – 10 | 2.5 | 4 | 6 | 9 | 15 | 22 | 36 | 58 |
| Over 10 – 18 | 3 | 5 | 8 | 11 | 18 | 27 | 43 | 70 |
| Over 18 – 30 | 4 | 6 | 9 | 13 | 21 | 33 | 52 | 84 |
| Over 30 – 50 | 4 | 7 | 11 | 16 | 25 | 39 | 62 | 100 |
| Over 50 – 80 | 5 | 8 | 13 | 19 | 30 | 46 | 74 | 120 |
| Over 80 – 120 | 6 | 10 | 15 | 22 | 35 | 54 | 87 | 140 |
| Over 120 – 180 | 8 | 12 | 18 | 25 | 40 | 63 | 100 | 160 |
| Over 180 – 250 | 10 | 14 | 20 | 29 | 46 | 72 | 115 | 185 |
| Over 250 – 315 | 12 | 16 | 23 | 32 | 52 | 81 | 130 | 210 |
| Over 315 – 400 | 13 | 18 | 25 | 36 | 57 | 89 | 140 | 230 |
| Over 400 – 500 | 15 | 20 | 27 | 40 | 63 | 97 | 155 | 250 |
All values in µm. Divide by 1,000 for millimetres.
Clearance, Transition & Interference Fits
ISO 286 classifies the mating condition by whether the assembled hole and shaft always have gap, may have gap or overlap, or always overlap before assembly.
The shaft is always smaller than the hole at MMC. Parts slide, rotate, or assemble freely. Examples: H9/d9 running fits, H7/g6 precision sliding, H7/h6 locational clearance.
Tolerance zones overlap—assembly may show slight clearance or light interference depending on actual produced sizes. Examples: H7/k6 and H7/n6 for accurate location without heavy press force.
The shaft is larger than the hole before assembly. Press, shrink, or drive fits create rigid joints. Examples: H7/p6 locational interference, H7/s6 and H7/u6 for permanent assemblies.
Preferred Hole-Basis Fits (ISO 286)
Hole basis keeps the bore on H and varies the shaft—standard reamers and gauges make this the default in most machine shops. These are the ISO 286-1 preferred combinations for clearance, transition, and interference fits.
| Fit | Hole | Shaft | Type | Typical application |
|---|---|---|---|---|
| H11/c11 | H11 | c11 | Clearance | Loose running fit for wide commercial tolerances on external members. |
| H9/d9 | H9 | d9 | Clearance | Free running—not for precision, but tolerates temperature variation and high speeds. |
| H8/f7 | H8 | f7 | Clearance | Close running on accurate machines at moderate speeds and journal pressures. |
| H7/g6 | H7 | g6 | Clearance | Sliding fit: moves and turns freely with accurate location—bearings, guide pins, precision slides. |
| H7/h6 | H7 | h6 | Clearance | Locational clearance: snug stationary fit, easy assembly and disassembly. |
| H7/k6 | H7 | k6 | Transition | Locational transition: accurate location with possible light interference. |
| H7/n6 | H7 | n6 | Transition | Locational transition with more interference permissible. |
| H7/p6 | H7 | p6 | Interference | Locational interference: rigidity and alignment without heavy bore pressure. |
| H7/s6 | H7 | s6 | Interference | Medium drive fit for steel parts or light-section shrink fits. |
| H7/u6 | H7 | u6 | Interference | Force fit for highly stressed parts; heavy press forces required. |
Preferred Shaft-Basis Fits (ISO 286)
Shaft basis fixes the external feature on h and adjusts the hole. Use when one shaft must mate with several bore tolerances—common in bearing applications, less common for general CNC parts.
| Fit | Hole | Shaft | Type | Typical application |
|---|---|---|---|---|
| D9/h9 | D9 | h9 | Clearance | Shaft-basis free running clearance mirror of H9/d9. |
| F8/h7 | F8 | h7 | Clearance | Shaft-basis close running fit. |
| G7/h6 | G7 | h6 | Clearance | Shaft-basis sliding / locational clearance mirror of H7/g6. |
| K7/h6 | K7 | h6 | Transition | Shaft-basis locational transition. |
| N7/h6 | N7 | h6 | Transition | Shaft-basis transition with greater interference risk. |
| P7/h6 | P7 | h6 | Interference | Shaft-basis locational interference. |
| S7/h6 | S7 | h6 | Interference | Shaft-basis medium drive interference. |
| U7/h6 | U7 | h6 | Interference | Shaft-basis force interference fit. |
ISO 286 Terminology
Key terms used on drawings, in inspection reports, and in the tables below.
Nominal size
The design dimension used to identify the feature—e.g. Ø25 in 25 H7/g6. Limits are derived from nominal + deviations.
Fundamental deviation
The letter (H, g, k, p…) positions the tolerance zone relative to nominal. Uppercase = hole, lowercase = shaft.
IT grade
International Tolerance number (IT4–IT18) defining zone width. Lower IT = tighter tolerance. IT7 and IT6 dominate precision machining.
Tolerance class
Letter + IT number without the IT prefix—H7, g6, p6. Specifies both zone position and width.
Hole basis
Hole tolerance fixed on H; shaft varied. Minimizes tool inventory—one H7 reamer, many shaft grind/hard-turn options.
Shaft basis
Shaft tolerance fixed on h; hole varied. Used when one shaft mates with multiple bore classes.
Quick answer: What fit should I specify?
ISO 286 controls mating hole and shaft limits — not general ± on every dimension. For undimensioned features, use ISO 2768 (typically ISO 2768-mK). Put H7/g6, H7/h6, or H7/p6 only on cylindrical joints that must slide, locate, or press together.
For most precision CNC assemblies, start with hole basis and H7/g6 if parts must slide with minimal play (bearings, bushings, guide pins). Use H7/h6 when parts locate but do not move. Step to H7/k6 or H7/n6 for tighter location without a press; use H7/p6 or H7/s6 when the joint must stay put without keys.
At 25 mm nominal, H7/g6 yields hole limits ≈ 25.000–25.013 mm and shaft ≈ 24.984–24.993 mm — clearance about +0.007 to +0.029 mm. PREMSA machines H7 bores and matched shafts daily in Monterrey for North American OEM assemblies.
Shop favourites: H7/g6 sliding · H7/h6 locational clearance · H7/k6 transition · H7/p6 press · H8/f7 close running · H9/d9 free running
How ISO 286 fits work in machining
Why hole basis wins in the shop
Reamers, boring bars, and CNC finishing tools produce holes to H7 quickly and repeatably. Adjusting the shaft (g6, h6, k6, p6) is cheaper than stocking multiple bore sizes. That is why drawings say 25 H7/g6 rather than 25 G7/h6 unless a shaft is shared across many bores.
ISO 286 vs ISO 2768
- ISO 2768: General tolerances when no local tolerance is shown—linear ± and simple geometry.
- ISO 286: Specific hole/shaft fits with limit sizes for mating cylindrical features.
- Together: Use ISO 286 on bearing bores and pins; ISO 2768-mK on the rest of the part.
IT grades and what they cost in the shop
IT4–IT6 need grinding, lapping, or precision boring—reserve for gauges, spindles, and high-load bearings. IT7 holes are everyday reamed or finish-bored bores. IT8–IT11 cover clearance running fits and non-critical shafts. The number in H7 or g6 is the IT grade: lower = tighter zone, higher machining and inspection cost.
Clearance, transition, and interference at a glance
- Clearance (H7/g6, H7/h6, H9/d9): Shaft always smaller than hole—sliding, running, or hand assembly.
- Transition (H7/k6, H7/n6): Zones overlap—accurate location; light press or slight clearance possible.
- Interference (H7/p6, H7/s6, H7/u6): Shaft larger than hole before assembly—press, shrink, or drive fit.
What to put on the drawing before quoting
Write the fit pair (Ø25 H7/g6), material, surface finish on mating faces (Ra 1.6 µm for precision bores is common), and whether CMM limit reports are required. If only one side is critical, note which part PREMSA machines. Pair with ISO 2768-mK for all other dimensions.
Popular fit lookups
Common questions machinists and designers search when specifying limits and fits:
- What are the limits for 25 mm H7/g6?
- At 25 mm (18–30 step): hole H7 ≈ 25.000–25.013 mm, shaft g6 ≈ 24.984–24.993 mm. Clearance about +0.007 to +0.029 mm—precision sliding fit.
- What is the difference between H7/g6 and H7/h6?
- Both are clearance fits on H7 holes. g6 leaves more play for sliding; h6 is tighter—locational clearance where parts stay put but assemble by hand.
- When do I use transition or interference fits?
- H7/k6 and H7/n6 are transition—accurate location, possible light press. H7/p6, H7/s6, and H7/u6 are interference for permanent or high-load joints.
- What are the limits for 10 mm H7/g6?
- In the 6–10 mm step: hole H7 ≈ 10.000–10.009 mm, shaft g6 ≈ 9.989–9.995 mm. Clearance roughly +0.005 to +0.020 mm—tighter absolute gap than 25 mm because IT zones scale with nominal size.
- Hole basis vs shaft basis — which should I use?
- Hole basis (H7/g6, H7/p6) fixes the bore on H and varies the shaft—one reamer, many fits. Shaft basis (G7/h6) fixes the shaft on h and varies the hole—use when one shaft mates several bore classes (bearing lines).
- What does IT7 mean in H7?
- The 7 is the IT grade from ISO 286-1—the tolerance zone width for that nominal size step. H7 = hole deviation H + IT7 width. IT6 shaft (g6) is tighter than IT7 hole—common pairing for precision sliding fits.
- ISO 286 vs ISO 2768 — same thing?
- No. ISO 2768 sets general ± defaults for undimensioned features. ISO 286 defines explicit hole/shaft limit pairs (H7/g6, etc.) for mating cylinders with clearance, transition, or interference.
- Is ISO 286 the same as ANSI B4.1?
- Close but not identical. Letter + IT logic matches, but limit values can differ ~0.1–0.5 thou on some pairs. Specify ISO 286 or ANSI on the drawing for Mexico–US production.
- What fit for a bearing bore?
- H7/g6 or H7/h6 for precision sliding bearings and bushings. H7/k6 when location is critical with minimal play. Match bearing catalog recommendations—some call H7 and leave shaft class to the supplier.
- Can I use ISO 286 on inch drawings?
- ISO 286 tables are metric. Convert inch nominal to mm for lookup, or dimension mating features in mm on CNC prints sent to metric shops. State inspection standard in the title block.
How to use this ISO 286 fit & tolerances chart
- PREMSA publishes this ISO 286 chart with IT grade tables, clearance–transition–interference cards, and preferred hole-basis / shaft-basis fit combinations for engineers quoting CNC work in Monterrey and North America.
- For 25 mm H7/g6 — one of the most common mating pairs on machined assemblies — hole limits are ≈ 25.000–25.013 mm and shaft ≈ 24.984–24.993 mm, yielding clearance about +0.007 to +0.029 mm.
- H7/g6 is the default precision sliding fit on bearing bores, guide pins, and bushings; H7/h6 when parts locate without intentional play; H7/p6 when press assembly is required.
- ISO 286 controls mating cylinder limits; ISO 2768-mK covers general ± on non-mating dimensions. Both belong on the same drawing—do not replace one with the other.
- For Mexico–US production, ISO 286 and ANSI B4.1/B4.2 are close but not identical (~0.1–0.5 thou on some pairs). State the inspection standard and critical fit pairs on the drawing before first-article inspection.
- For CNC quoting in Monterrey, send STEP plus drawing with fit callouts confirmed — request a quote or read the CNC tolerances guide.
Related engineering references
- Chart
ISO 2768 Tolerance Chart
General linear and geometric tolerances when individual limits are not shown on the drawing.
View chart - Chart
Surface Finish Chart
Ra values, ISO 1302 grades, and machining process guidance for mating surfaces.
View chart - Tool
Fit & Clearance Calculator
Calculate hole/shaft limits and assembly clearance for H7/g6, H7/h6, and other ISO 286 pairs.
Open tool - Tool
Tap & Drill Size Calculator
Thread and drill sizes for holes—complements ISO 286 bore tolerances on threaded features.
Open tool - Guide
CNC Design Guidelines
DFM guidance on tolerances, fits, and what to specify before quoting machined parts.
Read guide
ISO 286 fits: what engineers ask before specifying
- What is ISO 286 and when do I use it instead of ISO 2768?
- ISO 286 defines hole–shaft fits — limit sizes on mating cylinders (bearings, pins, bushings, guide shafts). ISO 2768 covers general tolerances on dimensions without individual limits (± on lengths, angles, basic geometry). In practice: ISO 2768-mK in the title block + H7/g6 (or another ISO 286 pair) on critical mating features.
- How do I read Ø25 H7/g6 on a drawing?
- 25 = nominal size (mm). H7 = hole class (H deviation, IT7 grade). g6 = shaft class (g deviation, IT6 grade). The slash separates hole (top) from shaft (bottom). Each part is machined within its tolerance zone; the resulting assembly falls into clearance, transition, or interference depending on actual produced sizes.
- What is the difference between clearance, transition, and interference fits?
- Clearance: the shaft always fits with gap (H7/g6, H7/h6, H9/d9)—sliding or hand assembly. Transition: zones overlap; slight clearance or light interference is possible (H7/k6, H7/n6)—accurate location without heavy press force. Interference: the shaft is larger than the hole before assembly (H7/p6, H7/s6, H7/u6)—press, shrink, or drive fit for rigid, permanent joints.
- Why do most drawings use hole basis (H) instead of shaft basis (h)?
- In hole basis, the bore stays on H (lower limit at nominal) and only the shaft changes—g6, h6, p6, etc. One H7 reamer, one finish bore tool, one gauge: same tooling for many fits. Shaft basis fixes the shaft on h and varies the hole—useful when one shaft mates with several bore classes (e.g. bearing lines), but requires per-class bore tooling. That is why H7/g6 dominates general machining.
- What does the number mean in H7, g6, or IT7?
- The letter positions the tolerance zone relative to nominal (H = hole from nominal upward; g = clearance shaft; p/s = interference). The number is the IT grade — zone width. Lower IT = tighter tolerance. IT6–IT8 are daily machining grades; IT7 hole + IT6 shaft (H7/g6) is the de facto standard for precision sliding fits.
- H7/g6 vs H7/h6 vs H7/k6 — which should I pick?
- H7/g6 — sliding with minimal play: bearings, guides, pistons, moving bushings. H7/h6 — same precision but no intentional gap; stationary parts that assemble by hand (alignment, centring). H7/k6 — transition; light rub on insert is possible; when location matters more than free slide. If the joint must not move without press force, step up to H7/p6 or H7/s6.
- What are the actual limits for 25 mm H7/g6?
- In the 18–30 mm step (ISO 286-2): H7 hole ≈ 25.000 – 25.013 mm; g6 shaft ≈ 24.984 – 24.993 mm. Clearance roughly +0.007 to +0.029 mm. Microns matter — process (reaming, grinding, measurement temperature) heavily affects first-article inspection.
- Does ISO 286 replace GD&T on the drawing?
- No. ISO 286 controls size (maximum and minimum diameter limits). GD&T (ISO 1101) controls form (roundness, cylindricity), orientation (perpendicularity), location (concentricity, position), and runout. An H7 bore perfect in diameter but oval or tilted will still fail in assembly. Precision joints need both: ISO 286 fit + geometric frames where applicable.
- Is ISO 286 the same as ANSI B4.1 in the US?
- Close, but not identical. ANSI B4.1/B4.2 and ISO 286 share letter + IT grade logic, but values can differ by ~0.1–0.5 thou (2.5–12 µm) on some pairs. For Mexico–US production, specify ISO 286 on the drawing or state the inspection standard to avoid first-article rejections.
- Common mistakes when quoting parts with ISO 286 fits
- 1) Defaulting H7/g6 everywhere without justification — drives reaming/grinding cost. 2) Forgetting ISO 2768 on non-mating dimensions. 3) Omitting material and measurement temperature (aluminium and steel measure differently on a CMM). 4) Mixing hole and shaft basis in one assembly without a note. 5) Requesting interference on thin walls or plastic — can crack under press. Review the stack in DFM before releasing an RFQ.
ISO 286 defines hole–shaft fits — limit sizes on mating cylinders (bearings, pins, bushings, guide shafts). ISO 2768 covers general tolerances on dimensions without individual limits (± on lengths, angles, basic geometry). In practice: ISO 2768-mK in the title block + H7/g6 (or another ISO 286 pair) on critical mating features.
25 = nominal size (mm). H7 = hole class (H deviation, IT7 grade). g6 = shaft class (g deviation, IT6 grade). The slash separates hole (top) from shaft (bottom). Each part is machined within its tolerance zone; the resulting assembly falls into clearance, transition, or interference depending on actual produced sizes.
Clearance: the shaft always fits with gap (H7/g6, H7/h6, H9/d9)—sliding or hand assembly. Transition: zones overlap; slight clearance or light interference is possible (H7/k6, H7/n6)—accurate location without heavy press force. Interference: the shaft is larger than the hole before assembly (H7/p6, H7/s6, H7/u6)—press, shrink, or drive fit for rigid, permanent joints.
In hole basis, the bore stays on H (lower limit at nominal) and only the shaft changes—g6, h6, p6, etc. One H7 reamer, one finish bore tool, one gauge: same tooling for many fits. Shaft basis fixes the shaft on h and varies the hole—useful when one shaft mates with several bore classes (e.g. bearing lines), but requires per-class bore tooling. That is why H7/g6 dominates general machining.
The letter positions the tolerance zone relative to nominal (H = hole from nominal upward; g = clearance shaft; p/s = interference). The number is the IT grade — zone width. Lower IT = tighter tolerance. IT6–IT8 are daily machining grades; IT7 hole + IT6 shaft (H7/g6) is the de facto standard for precision sliding fits.
H7/g6 — sliding with minimal play: bearings, guides, pistons, moving bushings. H7/h6 — same precision but no intentional gap; stationary parts that assemble by hand (alignment, centring). H7/k6 — transition; light rub on insert is possible; when location matters more than free slide. If the joint must not move without press force, step up to H7/p6 or H7/s6.
In the 18–30 mm step (ISO 286-2): H7 hole ≈ 25.000 – 25.013 mm; g6 shaft ≈ 24.984 – 24.993 mm. Clearance roughly +0.007 to +0.029 mm. Microns matter — process (reaming, grinding, measurement temperature) heavily affects first-article inspection.
No. ISO 286 controls size (maximum and minimum diameter limits). GD&T (ISO 1101) controls form (roundness, cylindricity), orientation (perpendicularity), location (concentricity, position), and runout. An H7 bore perfect in diameter but oval or tilted will still fail in assembly. Precision joints need both: ISO 286 fit + geometric frames where applicable.
Close, but not identical. ANSI B4.1/B4.2 and ISO 286 share letter + IT grade logic, but values can differ by ~0.1–0.5 thou (2.5–12 µm) on some pairs. For Mexico–US production, specify ISO 286 on the drawing or state the inspection standard to avoid first-article rejections.
1) Defaulting H7/g6 everywhere without justification — drives reaming/grinding cost. 2) Forgetting ISO 2768 on non-mating dimensions. 3) Omitting material and measurement temperature (aluminium and steel measure differently on a CMM). 4) Mixing hole and shaft basis in one assembly without a note. 5) Requesting interference on thin walls or plastic — can crack under press. Review the stack in DFM before releasing an RFQ.
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