ISO 286 Fit & Clearance Calculator
Calculate hole and shaft limit sizes, assembly clearance range, and fit category for ISO 286 mating pairs—H7/g6, H7/h6, H7/k6, H7/p6, and the rest of the shop standards.
Enter size and fit
Nominal diameter plus hole/shaft class—e.g. H7/g6 on the drawing.
Common fits
Precision sliding fit—the de facto standard for bearings and accurate location.
Limits & clearance
Deviations from nominal, limit diameters, and assembly clearance.
Ø25.0 mm H7/g6
Clearance fitShaft is always smaller than the hole at MMC—parts slide or assemble freely.
Assembly clearance
+0.007 mm – +0.029 mm
Tightest (min): +0.007 mm · Loosest (max): +0.029 mm
Tolerance zones relative to nominal (μm)
Bore · H7
- Deviation from nominal
- 0 / +13 µm
- Lower / Upper
- Limit diameter
- Ø25.000 – Ø25.013 mm
- Tolerance zone width
- 0.013 mm (13 µm)
Shaft · g6
- Deviation from nominal
- -16 / -7 µm
- Lower / Upper
- Limit diameter
- Ø24.984 – Ø24.993 mm
- Tolerance zone width
- 0.009 mm (9 µm)
ISO 286 table row: 18–30 mm.
Values follow ISO 286-1 fundamental deviations and IT grade tables (0.5–500 mm). Verify against your drawing, inspection method, and material temperature before releasing production.
Quick answer: how do you calculate ISO 286 clearance?
Enter the nominal diameter (mm) and the hole and shaft tolerance classes—e.g. H7 on the bore and g6 on the shaft. The calculator returns absolute limit sizes and the min/max assembly clearance (hole lower minus shaft upper, through hole upper minus shaft lower).
At 25 mm H7/g6 (18–30 mm ISO step), hole limits are 25.000–25.013 mm and shaft 24.984–24.993 mm—clearance +0.007 to +0.029 mm. That is the fit machinists quote daily for precision sliding assemblies.
Pair explicit ISO 286 fits on mating cylinders with ISO 2768 on general dimensions. PREMSA machines H7 bores and matched shafts in Monterrey for North American OEM work.
Common fits engineers look up first:
H7/g6 sliding · H7/h6 locational · H7/k6 transition · H7/p6 press · H8/f7 close running · H9/d9 free running
How to use the fit & clearance calculator
How assembly clearance is calculated
ISO 286 assigns each part its own tolerance zone relative to nominal. The hole zone sits above nominal for H-class bores; clearance shafts (g, h) sit below nominal. Assembly clearance is the gap between the smallest hole and the largest shaft (minimum clearance) and the largest hole and smallest shaft (maximum clearance).
If minimum clearance is positive, the fit is always clearance. If maximum is negative, it is always interference. When the range crosses zero, you have a transition fit—actual assembly depends on where each part lands inside its zone.
Hole basis vs shaft basis
Most North American and European shops use hole basis (H7/g6, H7/h6) because standard reamers and gauges fix the bore. Shaft basis (G7/h6) mirrors the same clearance with the shaft as the reference—useful when shaft stock is standardized.
- Hole basis: Vary the shaft, keep H on the bore—default for CNC machined assemblies.
- Shaft basis: Vary the hole, keep h on the shaft—common when shaft diameter is fixed.
- IT grade: Lower number = tighter zone = higher machining and inspection cost.
When to call out explicit fits on a drawing
Use ISO 286 limit fits wherever parts must mate with controlled play or press—bearings, pins, bushings, alignment features. Use ISO 2768-mK for everything else (overall length, width, non-mating surfaces).
Always state whether the fit is hole basis or shaft basis on the drawing. Ambiguous callouts are the #1 source of rework on cylindrical assemblies.
Popular ISO 286 fit lookups
Engineers search these hole–shaft pairs first. Values follow ISO 286-1 fundamental deviations and IT grades for the stated nominal size step.
- What is the clearance for 25 mm H7/g6?
- 18–30 mm step: hole H7 ≈ 25.000–25.013 mm; shaft g6 ≈ 24.984–24.993 mm. Assembly clearance ≈ +0.007 to +0.029 mm (clearance fit).
- What are the limits for 10 mm H7/g6?
- 6–10 mm step: hole H7 ≈ 10.000–10.009 mm; shaft g6 ≈ 9.989–9.995 mm. Clearance ≈ +0.005 to +0.020 mm.
- 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 is H7/k6 used?
- H7/k6 is a transition fit—possible light press or slight clearance depending on where each part lands in its zone. Common for accurate location with minimal play.
- When is H7/p6 used?
- H7/p6 is a medium interference press fit—permanent or semi-permanent joints where the shaft must not rotate or pull out without deliberate disassembly force.
- What does IT7 mean in H7?
- H is the hole deviation (zero lower limit for hole basis). 7 is the IT grade that sets tolerance zone width—IT7 at 25 mm is 13 µm. Lower IT number = tighter zone.
- ISO 286 vs ANSI B4.1 for US–Mexico production?
- ISO 286 (metric, letter + IT) is standard on European and global OEM prints. ANSI B4.1/B4.2 (inch, RC/LOC/FN) is common on US legacy drawings. Convert nominal to mm and map to the closest ISO fit class for CNC quoting.
- How do I pair ISO 286 with ISO 2768?
- Call ISO 286 limit fits on mating bores and shafts; use ISO 2768-mK on general length, width, and non-mating surfaces. Explicit fit callouts always override general tolerances.
ISO 286 fits for CNC quoting in Monterrey
- PREMSA publishes this ISO 286 Fit & Clearance Calculator alongside the full ISO 286 Fit & Tolerances Chart for IT grade tables and preferred hole-basis / shaft-basis combinations.
- For 25 mm H7/g6—one of the most common mating pairs—hole limits are 25.000–25.013 mm and shaft 24.984–24.993 mm, yielding clearance +0.007 to +0.029 mm in the 18–30 mm ISO step.
- PREMSA quotes H7/g6, H7/h6, and H7/k6 bores and shafts daily for automotive, medical, and industrial OEM assemblies in Monterrey. IT7 holes are finish-bored or reamed; IT6 shafts are finish-turned or ground.
- Pair ISO 286 fits on mating cylinders with ISO 2768-mK on general dimensions. Finish mating bores to Ra 1.6 µm or better when IT7 location matters.
- ANSI B4.1 inch fits on US legacy prints map to metric ISO classes—confirm hole basis vs shaft basis before CAM. Read the CNC tolerances guide for quoting strategy.
- For production CNC quoting in Monterrey, upload STEP with explicit fit callouts on mating features—request a quote for DFM review and accurate limits.
Related engineering resources
- Chart
ISO 286 Fit & Tolerances Chart
Full IT grade tables and preferred hole-basis / shaft-basis fit combinations.
View chart - Chart
ISO 2768 Tolerance Chart
General linear and geometric tolerances—pair with ISO 286 on mating features.
View chart - Chart
Surface Roughness Chart
Ra, Rz, RMS, and ISO 1302 N-grade conversion with CNC process reference.
View chart - Chart
Tap & Drill Size Chart
UNC, UNF, and metric tap drill table with clearance drills at 75% thread.
View chart - Chart
Drill Bit Size Chart
Number, letter, and fractional drill diameters in mm and inches.
View chart - Guide
CNC Design Guide
DFM for holes, threads, wall thickness, and tolerance strategy on machined parts.
Read guide
Fit & clearance calculator FAQ
- What does H7/g6 mean?
- H7/g6 is a hole-basis fit designation: H7 is the hole class (H fundamental deviation, IT7 tolerance width) and g6 is the shaft class (g deviation, IT6). The slash separates hole (first) from shaft (second). Each part is machined within its zone; assembly clearance falls between the calculated min and max.
- What is minimum vs maximum clearance?
- Minimum clearance = smallest hole limit minus largest shaft limit (worst-case tight assembly). Maximum clearance = largest hole minus smallest shaft (loosest assembly). Both must meet your functional requirements.
- Can I use this for inch parts?
- Yes—toggle inches in the calculator. Nominal converts to millimetres for ISO 286 table lookup; limit diameters and clearances display in inches. Tolerance deviations remain in µm per the standard.
- How is this different from ISO 2768?
- ISO 2768 sets general ± defaults for undimensioned features. ISO 286 defines explicit hole/shaft limit pairs for mating cylinders with clearance, transition, or interference.
- What is hole basis vs shaft basis?
- Hole basis (H7/g6) fixes the bore tolerance and varies the shaft—standard when reamers and gauges fix the hole. Shaft basis (G7/h6) fixes the shaft and varies the hole—common when shaft diameter is standardized stock.
- What is a transition fit?
- A transition fit occurs when the clearance range crosses zero—some assemblies may have slight gap, others light press, depending on actual hole and shaft sizes within their zones. H7/k6 and H7/n6 are common examples.
- What is an interference fit?
- Interference fits (H7/p6, H7/s6) have negative clearance—the shaft is larger than the hole before assembly. Assembly requires press, shrink, or drive force for permanent joints.
- Does temperature affect fit calculations?
- ISO 286 tables assume 20 °C reference. Large steel assemblies measured hot or cold can shift effective clearance—note inspection temperature on critical fits and allow margin for thermal expansion in service.
- What surface finish for H7 bores?
- IT7 location bores are typically reamed or bored to Ra 1.6 µm (N7) or better. Rougher finishes widen effective clearance and make first-article inspection harder to repeat.
- ISO 286 vs ANSI limits and fits?
- ISO 286 uses metric letter codes (H, g, p) and IT grades. ANSI B4.1 uses inch RC/LOC/FN categories. For cross-border production, convert nominal to mm and specify the ISO fit class on CNC prints sent to metric shops.
H7/g6 is a hole-basis fit designation: H7 is the hole class (H fundamental deviation, IT7 tolerance width) and g6 is the shaft class (g deviation, IT6). The slash separates hole (first) from shaft (second). Each part is machined within its zone; assembly clearance falls between the calculated min and max.
Minimum clearance = smallest hole limit minus largest shaft limit (worst-case tight assembly). Maximum clearance = largest hole minus smallest shaft (loosest assembly). Both must meet your functional requirements.
Yes—toggle inches in the calculator. Nominal converts to millimetres for ISO 286 table lookup; limit diameters and clearances display in inches. Tolerance deviations remain in µm per the standard.
ISO 2768 sets general ± defaults for undimensioned features. ISO 286 defines explicit hole/shaft limit pairs for mating cylinders with clearance, transition, or interference.
Hole basis (H7/g6) fixes the bore tolerance and varies the shaft—standard when reamers and gauges fix the hole. Shaft basis (G7/h6) fixes the shaft and varies the hole—common when shaft diameter is standardized stock.
A transition fit occurs when the clearance range crosses zero—some assemblies may have slight gap, others light press, depending on actual hole and shaft sizes within their zones. H7/k6 and H7/n6 are common examples.
Interference fits (H7/p6, H7/s6) have negative clearance—the shaft is larger than the hole before assembly. Assembly requires press, shrink, or drive force for permanent joints.
ISO 286 tables assume 20 °C reference. Large steel assemblies measured hot or cold can shift effective clearance—note inspection temperature on critical fits and allow margin for thermal expansion in service.
IT7 location bores are typically reamed or bored to Ra 1.6 µm (N7) or better. Rougher finishes widen effective clearance and make first-article inspection harder to repeat.
ISO 286 uses metric letter codes (H, g, p) and IT grades. ANSI B4.1 uses inch RC/LOC/FN categories. For cross-border production, convert nominal to mm and specify the ISO fit class on CNC prints sent to metric shops.
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