Calculadora de Ajuste H8/f7
Visual, interactive ISO 286 tolerance calculator to view min/max limits, clearance, transition and interference on shaft and hole fits such as H7/g6, H7/h6, H7/k6 or H7/p6.
Ajuste ISO 286
Hole
Class
H8
Shaft
Class
f7
Cross-section view of the fit
Tolerances visually exaggerated to make the type of fit clear.
Actual hole
50.000 a 50.039 mm
Tolerancia: 0.000 a 0.039 mm
Actual shaft
49.950 a 49.975 mm
Tolerancia: -0.050 a -0.025 mm
Holgura/apriete
0.025 a 0.089 mm
Difference between the allowed hole and the allowed shaft.
Giro libre
Preset H8/f7
Shafts with moderate rotation, bushings and lubricated bearings.
Quick reading
How to interpret it
Hole H8 and shaft f7. If the minimum clearance is negative there can be interference. If both clearances are positive there is always play.
There may be a small percentage of error against the official standard, since it isn't legal to reproduce the full ISO tables verbatim. Always validate with official ISO 286 and the controlled drawing before making critical parts.
H8/f7 fit: limits by diameter (ISO 286)
Giro libre. Shafts with moderate rotation, bushings and lubricated bearings.
Example at Ø25 mm: hole H8 from 0 to +33 µm and shaft f7 from -41 to -20 µm, which gives a clearance between 20 and 74 µm.
How it is made: the H8 hole (IT8) by reaming or boring; the f7 shaft (IT7) by fine turning or grinding. Check both with a plug gauge and a micrometer, not with a caliper.
How it is assembled: by hand, with no force; the parts slide or turn freely.
| Ø range (mm) | Hole H8 | Shaft f7 | Min. clearance | Max. clearance |
|---|---|---|---|---|
| 1–3 | 0 / +14 | -16 / -7 | +7 | +29 |
| 3–6 | 0 / +18 | -22 / -10 | +10 | +40 |
| 6–10 | 0 / +23 | -27 / -13 | +13 | +50 |
| 10–18 | 0 / +27 | -33 / -16 | +16 | +60 |
| 18–30 | 0 / +33 | -41 / -20 | +20 | +74 |
| 30–50 | 0 / +39 | -50 / -25 | +25 | +89 |
| 50–80 | 0 / +46 | -60 / -30 | +30 | +106 |
| 80–120 | 0 / +54 | -71 / -36 | +36 | +125 |
| 120–180 | 0 / +63 | -83 / -43 | +43 | +146 |
| 180–250 | 0 / +72 | -96 / -49 | +50 | +168 |
| 250–315 | 0 / +81 | -107 / -55 | +56 | +188 |
| 315–400 | 0 / +89 | -118 / -61 | +61 | +206 |
| 400–500 | 0 / +97 | -129 / -67 | +67 | +227 |
Mathematical formula of the ISO tolerance system
First the IT tolerance is obtained and then it is positioned according to the letter.
1. Anchura IT
i = 0,45 · ∛D + 0,001 · D
`D` is the mean diameter of the nominal range. The multiplier is then applied: IT6 = 10i, IT7 = 16i, IT8 = 25i, IT9 = 40i.
2. Position of the letter
H7, K11, g6, p6...
The letter places the area with respect to the nominal. Uppercase for hole (`ES/EI`) and lowercase for axis (`es/ei`).
3. Resultado de montaje
holgura = agujero - eje
If the minimum clearance is positive, it is a clearance fit. If the maximum is negative, it is an interference fit. If it crosses zero, it is a transition fit.
Hole
Shaft
Clearance
The IT formula is public and indicative; the fundamental deviations per letter are computed by the tool's engine. For critical production, always validate against official ISO 286 and the controlled drawing.
ISO fits most used on the shop floor
From the loosest to the tightest. Open the fit you need to see the hole and shaft deviations, the resulting clearance or interference and how to assemble it.
Fit H11/c11
Muy libre
Coarse joints, agricultural machinery, dirt or large thermal variations.
Fit H9/d9
Holgura amplia
Easy assembly, free rotation, dirt, temperature or less precise manufacturing.
Fit H8/f7
Giro libre
Shafts with moderate rotation, bushings and lubricated bearings.
Fit H7/g6
Precision sliding fit
Shafts sliding with little clearance, guides and precision fits.
Fit H7/h6
Clearance/location
Hand assembly with a very close or line-to-line fit.
Fit H7/js6
Centred transition
Centring with a possible small clearance or interference.
Fit H7/k6
Light transition
Precise centring with a possible light tap or small interference.
Fit H7/n6
Firm transition
Centring with a small interference; may need a light press.
Fit H7/p6
Apriete ligero
Light press fits, bushings or small pinions.
Fit H7/r6
Apriete medio
Press fits with good torque transmission and difficult disassembly.
Fit H7/s6
Apriete medio
Permanent joints using a press or a thermal difference.
Fit H7/u6
Apriete fuerte
Permanent assemblies, normally with a powerful press, heating or cooling.
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