Clearance fits

A clearance fit can have zero minimum size clearance. MISUMI includes H7/h6 in this family. Real sliding also depends on geometry, surface condition and assembly. MISUMI fit guidance

For nominal 20 mm H7/g6 in the cited MISUMI table, the hole is 20.000–20.021 mm and the shaft is 19.980–19.993 mm. Worst-case diametral clearance is 0.007–0.041 mm. This applies to the named size interval and classes, without form, orientation or location constraints.

ISO 286-1:2010 establishes concepts, terminology and the code system for linear-size tolerances. Its scope includes cylinders and two parallel opposite surfaces, and its fit terminology excludes orientation and location constraints. ISO 286-2:2010 supplies commonly used tolerance classes and limit deviations. A size-fit calculation is therefore one part of specifying a functional assembly. ISO 286-1, ISO 286-2

Calculate the limits before choosing a label

For cylindrical features, let Dmin and Dmax be accepted hole diameters, and dmin and dmax accepted shaft diameters. At the same reference condition:

These equations are worst-case size arithmetic: they combine opposite permitted extremes without assuming a production distribution. They do not predict the most common assembled clearance or justify a statistical acceptance claim.

Positive Cmin establishes positive size clearance under the assumptions. Negative Cmin with positive Cmax permits either clearance or interference, a transition fit. MISUMI fit families

For concentric, ideal cylinders, radial clearance is half the diametral clearance. A drawing or record that says only “clearance 0.02” leaves an important ambiguity. Specify which quantity is intended. An offset shaft can contact one side of a bore despite positive diametral clearance; diametral clearance is not a uniform gap around a loaded assembly.

Read the complete tolerance class

Read nominal size, letter and grade together. Uppercase denotes holes, lowercase shafts. H has zero lower deviation; h has zero upper deviation. Numerical tolerance width depends on size interval. MISUMI notation and tables

Preserve the referenced standard and size boundary when copying a table. ISO 286-2 identifies its tables as limit deviations for holes and shafts; the public scope does not replace the complete ordered standard or its corrigenda. Avoid combining a nominal size from one row with deviations from a neighboring interval. ISO 286-2 scope and corrigendum record

Bounded example: nominal 20 mm H7/g6

MISUMI's published JIS B 0401-2/ISO 286-2-based table uses the interval over 18 through 30 mm for this example:

Source: MISUMI tolerance table. The table is used for these named classes and this size interval, not as a universal fit recommendation.

Reconciled limit calculation:

• Cmin = 20.000 − 19.993 = 0.007 mm = 7 μm.
• Cmax = 20.021 − 19.980 = 0.041 mm = 41 μm.
• Range width = 41 − 7 = 34 μm, matching 21 + 13 μm from the two size tolerances.

The corresponding centered ideal radial clearance is 3.5–20.5 μm. These results establish a size-clearance range at the reference condition; they do not certify a particular force, running speed, lubricant film, positioning accuracy or leak rate.

Preserve clearance through processing and service

Identify whether dimensions apply before or after coating, heat treatment and final finishing. As original geometry, a uniform coating thickness t on a shaft increases its diameter by 2t; an inward coating of thickness t on a bore reduces its diameter by 2t. If both mating surfaces receive coatings, their radial thicknesses contribute separately to the reduction in diametral clearance. Use actual accepted coating limits and dimensional inspection, not nominal coating thickness alone.

Temperature can change fit in either direction. SKF's bearing-selection guidance explains that different component temperatures can loosen a shaft fit or obstruct intended axial movement in a housing; steady-state and transient conditions both matter. That guidance concerns bearing seats, but illustrates why room-temperature assembly clearance should not be assumed to persist unchanged in service. SKF selecting fits

Illustrative thermal sensitivity, not a material recommendation: assume a 20 mm shaft expands freely and uniformly with an assumed coefficient 12 × 10⁻⁶/K, while the bore stays unchanged. A 50 K shaft temperature rise increases diameter by approximately 20 × 12 × 10⁻⁶ × 50 = 0.012 mm. Starting from the example's minimum 0.007 mm clearance, the simplified model gives 0.007 − 0.012 = −0.005 mm. This warns of possible interference; it is not a coupled thermal/contact analysis or a claim about an identified assembly.

Bearing internal clearance is also different from clearance between a bearing ring and its seat. SKF explains that mounting interference and temperature differences affect internal clearance. Do not select a loose seat merely to preserve a desired internal-clearance number without reviewing ring load, creep and locating requirements. SKF bearing fit and internal-clearance discussion

Functional specification and inspection

Define the required motion or location, engagement length, loads, temperature range, lubrication and assembly conditions before selecting a class. Review form, surface texture, burrs, cleanliness, axis alignment and entry geometry separately. Several individually acceptable local size measurements need not prove that a long shaft passes freely through a distorted or misaligned bore.

Record hole and shaft limits with their units, governing standard, datum/axis requirements, final processing state and inspection basis. For interchangeable production, assess all permitted combinations; if selective pairing is intended, control and identify the matched sets. Measure and report against the accepted drawing rather than treating a successful hand assembly as proof of every dimensional requirement.

Source versions

Reviewed 2026-11-01, America/Los_Angeles. ISO identifies Part 1 edition 2, April 2010, and Part 2 edition 2, June 2010, both confirmed in 2026, with 2013 corrigenda listed. MISUMI's cited article prints 2026/10/26. The SKF extracts are used for bounded application guidance without assigning an independently verified technical edition. Original sensitivity calculations state their assumptions explicitly.

Part features