Approach Strategies for Holes
For IT7 tolerances or tighter (e.g. H7), drilling alone isn't enough. Leave 0.2-0.3 mm of stock and use a machine reamer. To guarantee absolute cylindricity on large diameters, boring is the safest option.
Calculadora de Ajuste H7/g6
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.
Mandatory notice
Notice before using the ISO 286 calculator
This calculator helps estimate ISO 286 tolerances for shaft and hole, visualise clearance, transition or interference fits, and prepare a first drawing read-through.
The calculation is derived from the formulas and nominal ranges of the ISO 286 system. It does not copy or reproduce official tables, so some values may differ by a few micrometres from the printed standard.
Do not use these results as the sole basis for manufacturing, accepting or rejecting critical parts. Always validate against the controlled drawing, the current official standard and your shop's quality/metrology criteria.
GetGCode is not affiliated with, authorised, licensed or endorsed by ISO. The tool is for educational and indicative use; any manufacturing decision remains the user's responsibility.
Ajuste ISO 286
Hole
Class
H7
IT1 more accurateIT18 more tolerance
Shaft
Class
g6
IT1 more accurateIT18 more tolerance
Cross-section view of the fit
Tolerances visually exaggerated to make the type of fit clear.
With clearance
Actual hole
50.000 a 50.025 mm
Tolerancia: 0.000 a 0.025 mm
Actual shaft
49.976 a 49.991 mm
Tolerancia: -0.024 a -0.009 mm
Holgura/apriete
0.009 a 0.049 mm
Difference between the allowed hole and the allowed shaft.
Deslizante preciso
Preset H7/g6
Shafts sliding with little clearance, guides and precision fits.
Quick reading
How to interpret it
Hole H7 and shaft g6. 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.
Practical Machining Guide for Tight Tolerances
Management of correctors (Wear) at the machine
If the total error budget is only a few microns, machine the finishing pass leaving 0.02 mm of stock. Measure the part on the machine and adjust the wear offset in the control before running the final pass.
Material behavior
Holding a g6 fit in aluminum is very different from doing it in Inconel or titanium. In heat-resistant alloys, tool deflection and edge wear call for lowering the cutting speed (Vc) and controlling the feed to avoid taper on the part.
The impact of thermal expansion
Precision metrology requires parts at room temperature. Measuring a freshly turned steel shaft will give a false dimension due to thermal expansion. Let the part cool before accepting a critical fit.
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
min. = nominal + EImax. = nominal + ES
Shaft
min. = nominal + eimax. = nominal + es
Clearance
min. = min. hole - max. shaftmax. = max. hole - min. shaft
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.
Frequently asked questions about ISO 286 tolerances and fits
What is the ISO 286 system of tolerances and adjustments?
The ISO 286 standard regulates tolerances, deviations and fits for cylindrical and smooth parts, such as shafts and holes. Defines maximum and minimum limits so that the fit between pieces is correct according to their mechanical function.
What is the difference between a loose, tight and transition fit?
In a clearance fit the hole is always larger than the shaft and allows movement. In an interference fit the shaft is larger than the hole and needs force, a press or temperature to assemble. In a transition fit the ranges overlap and you may end up with a small clearance or a small interference.
What does an H7/g6 mechanical setting mean?
H7/g6 is a precision running fit. H7 defines the hole tolerance zone in the basic-hole system, and g6 defines a shaft slightly below nominal. It is used where parts must slide or rotate with little play and good accuracy.
How do you machine an H7 hole in the workshop?
Drilling alone is usually not enough for an H7 hole. The normal route is to drill leaving about 0.2 to 0.3 mm of stock and finish with a machine reamer or by boring, especially when good cylindricity is required.
Why is it important to measure the part at room temperature?
Tight tolerances can come down to a few microns, and the thermal expansion of a freshly machined part can distort the reading. To validate a critical fit, let the part stabilise and measure with suitable instruments at controlled temperature.
How do you go from micrometers to millimeters in ISO tolerances?
To convert micrometres to millimetres you divide by 1000. For instance, 25 microns is 0.025 mm. The calculator shows the limits in millimetres so you can read them straight off the drawing and at the machine.
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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