Shaft Hole Fit Calculator — ISO 286

Picking the right fit between a shaft and a hole is a core part of mechanical design. Choose poorly and you’ll end up with assemblies that seize up, rattle from play, or wear out too early. The Shaft Hole Fit Calculator – ISO 286 lets you work out hole limits, shaft limits, and the type of fit (clearance, transition, or interference) based on nominal diameter, hole class, and shaft class. Choosing a proper fit is something you run into everywhere: in drivetrain parts, machinery, and measurement equipment—any place where two cylinders need to mate and function dependably. On this page, you’ll find the ISO 286 formulas, a practical example, a technical breakdown, and an FAQ.

What is shaft hole fit (ISO 286)?

“Shaft-hole fit” just means how much slack or tightness there is when you put a shaft into a hole. ISO 286 lays out the rules for exactly how much the two sizes can vary—so you end up with a slip fit, a push fit, or a press fit, no guesswork needed.

Simple Explanation

Imagine dropping a peg into a hole: if it drops in freely, that's a clearance fit. If you need to push hard or use a press, that’s an interference fit. ISO 286 defines standard tolerances, so you can specify how parts should be matched and know what sort of fit you’ll actually get after machining.

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📹 Video Walkthrough — How to Use This Calculator

How to Use This Calculator

1. Enter the nominal diameter of the shaft and hole in the Nominal Size (mm) field.
2. Select the appropriate tolerance class from the Hole Class dropdown (e.g., H7 for general engineering).
3. Select the shaft tolerance class from the Shaft Class dropdown (e.g., g6 for a sliding fit).
4. Click Calculate to see your result.

Mathematical Formulas

You’ll find the formulas for ISO 286 fits below. These are centered around the “basic tolerance unit” (i) and its multiples, which set the width of each tolerance band for a given fit and size.

The ISO 286 standard uses specific formulas to calculate tolerances and fits:

Simple Example

Inputs: Nominal size = 25 mm, Hole class = H7, Shaft class = h6

Basic tolerance unit: i = 0.45 × 25^1/3 + 0.001 × 25 ≈ 1.307 μm

H7 hole tolerance: 16 × 1.307 ≈ 20.9 μm → Hole limits: 25.000 to 25.021 mm

h6 shaft tolerance: 10 × 1.307 ≈ 13.1 μm → Shaft limits: 24.987 to 25.000 mm

Result: Clearance fit — 0.000 to 0.034 mm clearance.

Understanding ISO 286 Fits

ISO 286 sets up a system for deciding clearances and tolerances between mating cylindrical parts. This calculator helps you apply those rules to get limits for parts that should go together with the fit you want, using the same letter/number system from the standard. Each part gets a tolerance “zone” — letters set its position (above or below nominal), numbers set its width (tolerance grade).

For holes, the “H” classes are most common, because standard tools make it straightforward to get the nominal size. Shaft letters vary: “h” is centered around the nominal, and others like “f”, “g”, “k”, etc., shift the tolerance zone below or above the nominal to get different fits. Pairing the proper shaft and hole classes will give you predictable fits for assembly—nothing is guaranteed in the shop, but ISO 286 is about as close as you’ll get for interchangeability.

Tolerance Classes and Their Meanings

For holes, H6 is for very precise work, H7 is common general-purpose, and H8/9/10 are for looser fits when high accuracy isn’t needed. For shafts, the fundamental deviation letter (f, h, k, etc.) shifts the tolerance zone up or down in relation to nominal. You select a combination based on function, not only on “tight” or “loose.”

• H6: Tight, for high precision
• H7: General engineering
• H8: For routine assembly/machining
• H9-H11: For less critical fits

Shaft letters move the size zone below (f/g), on (h), or above (j/k/m/n/p/r/s) the nominal, varying the fit. Each combination shifts the assembly toward clearance or interference.

Practical Applications

Engineers use ISO 286 shaft-hole fits across lots of common equipment—anywhere lasting, correct assembly matters:

Automotive Engineering

Auto components—bearings, pistons, gearbox parts—are all dependent on reliable fits. If you’re designing actuator mounts, for example, keeping hole tolerances practical helps with straightforward assembly and less rework.

Manufacturing and Assembly

When you need parts made by different vendors to fit together, standardized fits prevent headaches at the assembly line. By calculating tolerance zones up front, you can set meaningful inspection requirements and keep things interchangeable.

Precision Instrumentation

For measurement tools or instruments, loose fits aren’t an option. H6/h6 is a go-to when you want minimal play. If you expect some thermal growth, using a bit more clearance (H7/g6) keeps assemblies functional as temperatures change.

Worked Example

Say you have a 30mm shaft and a matching hole. Here’s how to break it down using ISO 286:

Design Considerations and Best Practices

When you’re picking a fit, don’t just focus on numbers—think about how you’ll make and assemble the parts, what sort of loads they’ll see, and what’s likely to give you trouble down the line. Here are some pointers:

Manufacturing Capabilities

Fine tolerances cost more—tighter IT grades mean more setup time, more scrapped parts, slower throughput. Standard machining handles IT8–IT9; if you want IT6 or better, you’re likely paying for grinding. Don’t overspecify—use the loosest fit you can get away with for your function.

Assembly Requirements

If it’s meant to be pressed, specify an interference. Need it to move? Go for clearance. Most real-world mounting holes—like in actuator end brackets—are made to H7, H8, or sometimes H9, and generous fits like H8/f7 let you play with position during install.

Operating Conditions

Think about how the application changes under load and with temperature swings. Running fits may need more clearance if one or both parts heat up a lot. Dynamic loading calls for fits that can take some movement without coming apart or wearing fast.

Material Considerations

If you’re combining different metals (steel shaft, aluminum housing), watch out for differing thermal growth. What fits at room temp might go tight or loose during operation—you may need to adjust your original spec or factor in actual running conditions.

Related Calculations

No fit calculation works in isolation—you may also need to check for load ratings, possible stress risers, or a bit of extra clearance for temperature changes. If you’re building assemblies with bearings or press fits, double-check with those other calculators for a complete design perspective.

Quality Control

It’s not enough to calculate a fit—you have to measure finished parts to be sure you got what you intended. Plan for checking with micrometers, plug gauges, or a CMM if you’re serious about qualifying your process.

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