Fit
-Clearance (+) / interference (−)
-Fit tolerance
-Limits
| Upper dev. | Lower dev. | Max limit | Min limit |
|---|
Deviations in µm (1 µm = 0.001 mm ≈ 0.00004 in). Limits in mm, inch values below.
Tolerance zones
Standard tolerance grades for this size
How the calculator works
ISO 286-1 describes every tolerance zone with a letter and a number. The number is the standard tolerance grade (IT1 to IT18): how wide the zone is. The letter is the fundamental deviation: where the zone sits relative to the nominal size. Capital letters are holes, lower-case letters are shafts.
- Size range. Sizes are grouped into ranges (over 18 up to and including 30 mm, and so on). Each range uses the geometric mean of its limits, D = √(D1·D2), in mm.
- Tolerance factor. i = 0.45·∛D + 0.001·D (µm). The grades are multiples of it: IT6 ≈ 10i, IT7 ≈ 16i, IT8 ≈ 25i, IT9 ≈ 40i, IT11 ≈ 100i, each grade about 1.6 times the one before. The standard rounds these values, and in the smallest ranges uses conventional values, so the calculator uses the standard’s rounded results rather than the raw formula.
- Fundamental deviation. Shafts a to h have a negative upper deviation es (for example g: es ≈ −2.5·D0.34, f: ≈ −5.5·D0.41); h is zero. Shafts k to u have a positive lower deviation ei (for example n: ≈ 5·D0.34, m: IT7 − IT6). The other limit is the deviation plus or minus the IT value.
- Holes mirror the shafts: A to H have lower deviation EI = −es. For K, M and N up to IT8 and P to U up to IT7, ES = −ei + Δ, where Δ = ITn − ITn−1, so that H7/p6 and P7/h6 give the same fit. JS and js are symmetric: ±IT/2.
- Fit. Maximum clearance = largest hole − smallest shaft; minimum clearance = smallest hole − largest shaft. A negative clearance is interference.
The values were checked against independently published ISO 286-2 limits for every letter the calculator offers. If a combination is not defined by the standard (for example t up to 24 mm) or not offered here (for example K and M above IT8), the calculator says so instead of guessing. JS and js are calculated as exactly ±IT/2 as in ISO 286-1:2010; some older printed tables round odd IT7 to IT11 values down, so they can differ by 0.5 µm.
Worked example: Ø25 H7/g6
25 mm falls in the range over 18 up to 30 mm. IT7 = 21 µm and IT6 = 13 µm. The H7 hole has EI = 0, so ES = +21 µm: the hole is 25.000 to 25.021 mm. The g shaft has es = −7 µm, so ei = −7 − 13 = −20 µm: the shaft is 24.980 to 24.993 mm. Maximum clearance = 25.021 − 24.980 = 0.041 mm; minimum clearance = 25.000 − 24.993 = 0.007 mm. Always a clearance: a close sliding fit. In inch: hole 0.9843 to 0.9851 in, shaft 0.9835 to 0.9840 in.
Choosing a fit
| Hole basis | Shaft basis | Type | Typical use |
|---|---|---|---|
| H11/c11 | C11/h11 | Loose running | Wide commercial tolerances, parts that must assemble easily, dirty conditions |
| H9/d9 | D9/h9 | Free running | Large temperature changes, high running speeds or heavy journal pressure |
| H8/f7 | F8/h7 | Close running | Accurate running on lubricated shafts at moderate speed, accurate location |
| H7/g6 | G7/h6 | Sliding | Parts that slide and turn freely but locate accurately, not for running |
| H7/h6 | H7/h6 | Locational clearance | Snug fit for stationary parts that can still be assembled and taken apart freely |
| H7/k6 | K7/h6 | Locational transition | Accurate location, a compromise between clearance and interference |
| H7/n6 | N7/h6 | Locational transition | More accurate location where more interference is acceptable |
| H7/p6 | P7/h6 | Locational interference | Rigid, accurate location without special bore pressure requirements |
| H7/s6 | S7/h6 | Medium drive | Ordinary steel parts, shrink fits on light sections, tightest fit usable with cast iron |
| H7/u6 | U7/h6 | Force | Highly stressed parts, or shrink fits where heavy pressing forces are impractical |
The interference fits above transmit torque by friction. To size one properly you also need the contact pressure, the stresses in the hub and the assembly force or heating temperature: that depends on the materials and the hub outside diameter, not only on the fit. The interference fit calculator does exactly that: contact pressure, torque capacity, pressing force, stresses and shrink-fit temperature for these fits.
New to fit codes? Read H7/g6 fit explained for what the letters and numbers mean and how common fits compare.
Questions
What does H7/g6 mean?
H7/g6 is a hole-basis fit. The hole has fundamental deviation H (lower deviation zero) and tolerance grade IT7; the shaft has fundamental deviation g (slightly below the nominal size) and grade IT6. It is a close clearance fit used for sliding and locating parts. For 25 mm the hole is 25.000 to 25.021 mm and the shaft is 24.980 to 24.993 mm, giving 0.007 to 0.041 mm clearance.
Is ANSI B4.2 the same as ISO 286?
Yes for the numbers. ANSI B4.2 adopts the ISO system of limits and fits for metric sizes, so H7/g6 gives the same limits under both. The older inch standard ANSI B4.1 (RC, LC, LT, LN and FN classes) is a different system.
What is the difference between a clearance, transition and interference fit?
In a clearance fit the smallest hole is always larger than the largest shaft. In an interference fit the largest hole is always smaller than the smallest shaft, so the parts must be pressed or shrunk together. A transition fit can give either a small clearance or a small interference depending on where the actual parts fall in their tolerance zones.
Hole basis or shaft basis: which should I use?
Hole basis (H holes) is the usual choice because holes are made with fixed-size reamers and gauges while shafts are easy to grind to any size. Shaft basis (h shafts) suits bright drawn bar or a single shaft carrying several parts with different fits.
Can I enter an inch size?
Yes. Choose inch: the size is converted to millimetres (1 in = 25.4 mm) to find the ISO size range, and every limit is shown in both units. For inch-designed parts toleranced to ANSI B4.1 classes (RC, LC, FN) the limits are different.
Engineering aid for guidance. Check critical fits against the current edition of ISO 286-2 or ANSI B4.2 and your own design rules; you remain responsible for the design. Size range: over 0 up to 500 mm. Nothing you enter leaves your browser except through a share link you copy yourself.