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CORE LINKS · DESIGN GUIDES

Check a hole and shaft fit

A nominal 20 mm hole and shaft both have size ranges. Compare their tightest and loosest combinations to understand the fit.

Axial section of a clearance fit, showing hole diameter D, shaft diameter d and C equals D minus d.dDC = D − dDiametral clearance · gap exaggerated
Axial section of a clearance fit with exaggerated gaps. C = D − d is diametral clearance; for concentric parts the radial gap on each side is C/2.

What you will understand

  • Identify hole and shaft size ranges
  • Find minimum and maximum clearance
  • Distinguish fit classification from real assembly

Blue: defined conditions · Red: calculated quantities. Diagrams are schematic.

  • D: hole diameter / d: shaft diameter
  • C: diametral difference; negative means interference

The examples below are illustrative. Each example button loads its fixed values, units and mode. Ordinary calculator links do not load an example.

Read nominal dimensions as actual limits

Use the nominal size and upper/lower deviations to obtain each size limit. Check signs and distinguish mm from μm.

  • List Dmin/Dmax for the hole and dmin/dmax for the shaft
  • Check that minimum and maximum are ordered correctly
  • For JIS/ISO designations, verify deviations for the actual size and grade

Find the tightest and loosest combinations

Minimum clearance is the smallest hole minus largest shaft. Maximum clearance is the largest hole minus smallest shaft. The magnitude of negative clearance is interference.

  • Cmin > 0: the entered size ranges always have clearance
  • Cmax < 0: the entered size ranges always have interference
  • A range crossing zero can produce either; zero is the contact boundary
For practical review

These are diametral differences. They do not alone establish radial positioning, tilt, roundness or cylindricity. Check geometric tolerances and contact conditions separately.

Cmin = Dmin − dmax, Cmax = Dmax − dmin

Compare the values with the intended function

A clearance fit is not automatically suitable. Define acceptable limits for the purpose: rotation, positioning, force transmission or disassembly.

Example: hole and shaft near 20 mm

Inputs

  • Hole: Dmin = 20.000 mm, Dmax = 20.021 mm
  • Shaft: dmin = 19.980 mm, dmax = 19.993 mm

Results

  • Minimum clearance Cmin = 0.007 mm = 7 μm
  • Maximum clearance Cmax = 0.041 mm = 41 μm

The entered range is a clearance fit. This example does not automatically apply a JIS/ISO tolerance table. Whether 41 μm maximum clearance meets the required precision is a separate question.

Load the fixed values, units and mode for this illustration. Then edit them for your conditions.

Check temperature, form and assembly separately

Temperature differences, form, roughness or debris can obstruct assembly even with nominal clearance. An interference fit also requires press-fit stress and assembly-force checks.

  • Reference/operating temperatures and both materials
  • Roundness, cylindricity, roughness, chamfers, burrs and cleanliness
  • Function and requirements of the bearing, hub or mating part
  • Pressing, thermal assembly/disassembly methods and actual measurements

Keep a review checklist

This checklist is a personal reminder, not a safety score or an automatic approval. It is not sent or saved.

Continue with another guide

Reference information and illustrative calculations. This content does not guarantee suitability or safety of a design. Confirm the actual materials, component specifications and operating conditions.