AtlasCalcsUtility Calculation Suite
2026-07-30 8 min

Interference Fit Calculator

Calculate interference fit parameters per ISO 286. Compute max/min interference, average interference, and fit grade for press/shrink fits.

Calculator

Unit System
Nominal Diameter (mm)
Hole Tolerance
Shaft Tolerance

Results

Caution

Max Interference

37.9026mm

Maximum negative gap (tightest fit) at MMC

Min Interference

-17.0705mm

Minimum interference (loosest fit) at LMC

Avg Interference

10.4160mm

Average expected interference for nominal assembly

Hole Tolerance

33.5202mm

Total tolerance zone width for hole

Shaft Tolerance

21.4529mm

Total tolerance zone width for shaft

Fit Type

Transition

Classification: interference, transition, or clearance

Visualizations

Results Overview

37.9mmMax Interference
10.4mmAvg Interference
33.5mmHole Tolerance
21.5mmShaft Tolerance

Formula

Interference (press) fit analysis per ISO 286-1:2010. Max interference occurs at maximum shaft size and minimum hole size. Min interference at minimum shaft and maximum hole.

Max_Interference = Shaft_upperDev - Hole_lowerDev, Min_Interference = Shaft_lowerDev - Hole_upperDev

Alternative Form

Avg_Interference = (Max_Int + Min_Int) / 2

Variables

SymbolNameUnitDescription
Int_maxMax InterferencemmMaximum possible interference (tightest fit)
Int_minMin InterferencemmMinimum possible interference (loosest fit)
Shaft_upperShaft Upper DevmmUpper deviation of shaft tolerance zone (es)
Hole_lowerHole Lower DevmmLower deviation of hole tolerance zone (EI)

Explanation

In an interference fit, the shaft tolerance zone lies entirely above the hole tolerance zone, ensuring that the shaft is always larger than the hole. Assembly requires force (press fit) or thermal expansion/contraction (shrink fit).

Derivation

ISO 286 defines fundamental deviations for shafts p, r, s, t, u which place the shaft tolerance zone above the zero line (positive deviations), while the H hole has lower deviation at zero. The resulting interference is the difference between shaft and hole sizes.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Enter nominal diameter and select hole tolerance grade.

Nominal Diameter:25 mm
Hole:H7
Result: Hole zone: 0.0000/33.5202 mm
Step 2

Select shaft tolerance grade for interference fit.

Shaft:p6
Result: Shaft zone: 16.4497/37.9026 mm
Step 3

Compute interference values.

Max Int = es - EI, Min Int = ei - ES
Max Interference:37.9026 mm
Min Interference:-17.0705 mm
Intermediate: Max Int = 37.9026 - 0.0000 = 37.9026
Result: Fit: Transition, Avg Int: 10.4160 mm
Final Answer
37.9026

Worked Examples

See how the calculator works with different scenarios.

Scenario

A light press fit for a 25 mm diameter shaft in a gear or bearing. H7/p6 is the most common light press fit design.

Inputs

Nominal Diameter:25 mm
Hole:H7
Shaft:p6

Calculation

i = 0.45×∛25 + 0.001×25 = 1.31 µm IT7 = 16×1.31 = 21 µm IT6 = 10×1.31 = 13 µm p6 lower = 0.6×(IT6^1.08) ≈ 8 µm Max Int = 21 - 0 = 21 µm Min Int = 8 - 21 = -13 µm (actually transition at extreme)

Result

Min Interference: 0 µm, Max Interference: 21 µm

Interpretation

H7/p6 gives a light press fit suitable for parts that need moderate torque transmission with a press.

Understanding Your Result

Your Result: Max Interference: 37.9026 mm

Typical range: H7/p6: 0-22 µm (light press). H7/s6: 0-34 µm (heavy press). H7/u7: 8-45 µm (force fit). H7/t6: 0-28 µm (medium press). H7/r6: 0-18 µm (light interference).

What This Means

An interference fit (press fit or shrink fit) ensures the shaft is always larger than the hole, creating a compressive radial stress that holds parts together without additional fasteners.

Why It Matters

Interference fits provide reliable torque transmission, eliminate fretting, maintain concentricity, and reduce part count by removing the need for keys or set screws.

Professional Interpretation

Interference fits are classified by assembly method: press fits (p, r) for light interference using mechanical force, and shrink fits (s, t, u) for heavy interference requiring thermal assembly.

Recommendations

  • •Use H7/p6 for light press fits with moderate torque requirements
  • •Use H7/s6 for heavy press fits with high torque transmission
  • •Use H7/u7 only for shrink fits where thermal expansion is used for assembly
  • •Calculate assembly force required based on interference and friction coefficient
  • •Consider hoop stress in the hub to prevent yielding
  • •Verify that assembly does not exceed material yield strength
  • •Use surface finish fine enough to prevent galling during assembly

Educational Content

Introduction

An interference fit (also called a press fit or friction fit) is a fastening method where the shaft is intentionally made larger than the hole, creating compressive stresses that hold the assembly together.

Concept Explanation

The interference creates radial pressure at the mating surface, proportional to the interference magnitude, part diameters, and material properties. The friction force transfers torque and axial loads.

Applications

▸Gear-to-shaft connections
▸Bearing-to-housing mounts
▸Bushing/sleeve installation
▸Rotor-to-shaft assemblies
▸Valve seat installations
▸Wheel-to-axle press fits
▸Permanent mechanical joints

Benefits

  • •Eliminates need for keys, splines, or fasteners
  • •Provides high torque transmission capacity
  • •Ensures concentric alignment
  • •Reduces part count and assembly complexity
  • •Prevents fretting and backlash
  • •Handles shock loads well

Limitations

  • •Difficult to disassemble without damage
  • •Requires careful control of tolerances
  • •May cause stress concentrations
  • •Requires thermal or mechanical assembly equipment
  • •Hub yielding risk at high interference

Best Practices

  • •Use shrink fit (heat hub) for high interference rather than force assembly
  • •Calculate maximum hoop stress to avoid yielding the hub
  • •Provide assembly chamfers on both shaft and hole
  • •Use lubricant to reduce assembly force and prevent galling
  • •Verify assembled dimensions after press fit (hole may expand)
  • •Consider stress relaxation over time for polymer components

Common Misconceptions

Myth: More interference always means a stronger joint.
Truth: Excessive interference can yield the hub, reducing retained interference and joint strength.
Myth: Press fits are permanent and cannot be disassembled.
Truth: With hydraulic pressure or thermal techniques, many press fits can be disassembled without damage.
Myth: Interference fits do not need surface finish control.
Truth: Rough surfaces reduce effective interference and can cause galling during assembly.

Practical Tips

  • •Calculate assembly force using F = P × A × µ where P = contact pressure from interference
  • •For shrink fits, hub temperature increase should not exceed material tempering temperature
  • •Use shaft cooling (dry ice) combined with hub heating to reduce differential expansion needed
  • •Specify maximum assembly force to protect bearings and other press-fit components
  • •Consider stress relaxation at elevated operating temperatures
  • •Verify hub wall thickness is adequate (ratio > 0.5 of shaft diameter recommended)
  • •For thin-walled hubs, use FEA to verify stress distribution

Common Mistakes

Choosing too much interference causing hub yielding
Calculate hoop stress using thick-wall cylinder theory. Keep stress below 60-80% of material yield strength.
Not accounting for thermal expansion during operation
If operating temperature differs from assembly temperature, calculate differential expansion and adjust fit selection.
Ignoring stress concentrations at hub edges
Use generous radii and chamfers at hub ends. Consider stress concentration factor of 2-3 at edges.
Using press fit for thin-walled or brittle materials
Cast iron, ceramics, and thin-walled polymers may crack under press fit stresses. Use shrink fit or adhesive bonding instead.

Assumptions

This calculator makes the following assumptions to provide estimates:

Elastic Deformation: Both parts assumed to remain in the elastic range. Plastic deformation reduces retained interference.
Room Temperature Assembly: Standard calculation assumes 20°C reference. Thermal assembly requires separate thermal expansion compensation.
Uniform Contact Pressure: Assumes perfect cylindrical contact. Form errors reduce effective contact area and load capacity.
No Stress Relaxation: Long-term stress relaxation (especially in polymers) is not considered.

Limitations

Be aware of these limitations when using this calculator:

Approximated Deviations: Shaft deviations for p, r, s, t, u positions are approximated. Exact ISO 286 table values may vary slightly.
No Stress Calculation: This calculator computes interference magnitude but not the resulting stress or assembly force.
Limited Shaft Grades: Only interference-producing shaft positions (p, r, s, t, u) are included.
Static Analysis Only: Dynamic effects, fatigue, and vibration loosening are not considered.

Frequently Asked Questions

Answers to common questions about this calculator.

What is an interference fit?
An interference fit is a mechanical joint where the shaft is intentionally larger than the hole, creating compressive stress that holds the assembly together without additional fasteners.
What is the difference between press fit and shrink fit?
Press fit uses mechanical force (press) to assemble. Shrink fit uses thermal expansion/contraction (heat the hub, cool the shaft) for assembly with higher interference.
How is interference fit calculated?
Max Interference = Shaft_UpperDev - Hole_LowerDev. Min Interference = Shaft_LowerDev - Hole_UpperDev. Both at their respective MMC conditions.
What does H7/p6 mean?
H7 is a hole with H fundamental deviation (lower dev = 0) and IT7 grade. p6 is a shaft with p deviation (positive) and IT6 grade. This is a common light press fit.
What is the most common interference fit?
H7/p6 is the most common light press fit, used for bearings, bushings, and gears. H7/s6 is used for heavy press fits.
How do I assemble an interference fit?
For light interference: mechanical press with lubricant. For heavy interference: heat the hub (150-300°C), cool the shaft (dry ice), or both.
Can interference fit transfer torque?
Yes. Torque capacity = interference_pressure × contact_area × friction_coefficient × radius. The friction force resists relative rotation.
What materials are suitable for interference fits?
Steel, stainless steel, cast iron (careful), bronze, and aluminum. Brittle materials require careful stress analysis.
How does surface finish affect interference?
Rough surfaces reduce effective interference as peaks are crushed during assembly. For precision fits, Ra ≤ 0.8 µm is recommended.
What is the maximum recommended interference?
Maximum interference is limited by material yield strength. General guideline: keep hoop stress below 80% of yield strength.
How do I calculate press fit assembly force?
F = µ × P × A where µ = friction coefficient (0.1-0.2 for steel), P = contact pressure, A = contact area. P is calculated from interference using thick-wall cylinder theory.
What is the H7/s6 fit used for?
H7/s6 (heavy press fit) is used for gears on shafts, large bearing installations, and applications requiring high torque transmission without keys.
How much to heat a hub for shrink fit?
Temperature increase required: ΔT = (interference + assembly_clearance) / (α × D) where α = CTE (~12×10⁻⁶/°C for steel). Typical heating: 150-300°C.
Can interference fits be disassembled?
Yes, using hydraulic pressure (oil injection method), thermal disassembly, or mechanical pullers. Some disassembly methods risk surface damage.
What is the stress in interference fits?
Radial pressure creates tangential (hoop) stress in the hub and compressive stress in the shaft. Use Lamé equations for thick-wall cylinders to calculate.
What is H7/u7 fit?
H7/u7 is a very heavy force fit with guaranteed interference. Suitable for permanent assemblies requiring maximum torque transmission.
How does operating temperature affect interference?
If the hub and shaft have different coefficients of thermal expansion, operating temperature changes will alter the interference. Calculate for worst-case conditions.
What is the difference between p6 and s6 shafts?
Both are IT6 grade, but p6 has smaller positive deviation (light press) while s6 has larger positive deviation (heavy press). s6 gives more interference.
How does rotational speed affect interference fits?
At high speeds, centrifugal force can reduce radial pressure. For very high-speed applications, verify that retained interference is adequate at operating speed.
Can I use interference fit with aluminum?
Yes, but aluminum's higher CTE means interference changes more with temperature. Use tighter fits or shrink assembly to avoid galling.
What is the minimum wall thickness for hubs?
Minimum hub outer diameter should be at least 2× shaft diameter for adequate strength. Thinner walls require closer tolerance control and stress analysis.
How do I specify interference fit on a drawing?
Use ISO notation: e.g., ø25 H7/p6. On the hole: ø25 H7 (ø25.000/ø25.021). On the shaft: ø25 p6 (ø25.022/ø25.035).
What is the corrosion risk in interference fits?
Fretting corrosion can occur at the interface of press fits under cyclic loading. Use anti-seize compounds or surface treatments to reduce risk.
How does the length of engagement affect fit?
Longer engagement increases total force capacity but makes assembly more difficult. The interference per diameter is independent of length.
What is the RoJ (Ring of Junkers) effect?
Named after a researcher, it describes stress distribution at hub ends where local stress concentration is 2-3× the nominal. Use generous radii to mitigate.
Can I combine interference fit with adhesive?
Yes, Loctite retaining compounds can supplement interference fits, especially for looser fits or to seal the joint against corrosion.
What is the role of lubrication in press fits?
Lubricant reduces assembly force by 20-40%, prevents galling, and provides more consistent assembly results. Use MoS₂ or white assembly paste.
How does interference affect bearing clearance?
Pressing a bearing into a housing reduces internal clearance. Account for this reduction (typically 60-80% of interference affects bearing radial clearance).
What are the alternatives to interference fits?
Keys, splines, set screws, taper fits, adhesive bonding, and clamping arrangements can replace interference fits where disassembly is needed.
How do I measure interference?
Measure shaft OD and hole ID separately at controlled temperature. Interference = shaft size - hole size. In-place measurement is more complex.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

Force Fit
An interference fit requiring mechanical force for assembly (also called press fit).
Fretting Corrosion
Surface damage at the interface of tightly fitting parts under cyclic loading.
Hoop Stress
Circumferential tensile stress in the hub caused by interference pressure (tangential stress).
Hub
The outer part (typically with a hole) that receives the shaft in an interference fit assembly.
Interference
The amount by which the shaft exceeds the hole size, creating compressive radial pressure.
Lamé Equations
Thick-wall cylinder stress formulas used to calculate radial and tangential stresses in interference fits.
MMC
Maximum Material Condition - condition of maximum shaft size and minimum hole size (maximum interference).
Press Fit
Assembly method using axial mechanical force to insert a larger shaft into a smaller hole.
Retained Interference
The actual interference remaining after elastic deformation during assembly.
Shrink Fit
Assembly method using thermal expansion (heating hub, cooling shaft) to create temporary clearance.
Stress Concentration
Local stress increase at geometric discontinuities like hub edges, typically 2-3× nominal stress.
Thick-Wall Cylinder
A cylinder with wall thickness > 1/10 of radius, requiring Lamé stress analysis rather than thin-wall approximation.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

ISO 286-1ISO 286-2ISO 2768-1ASME Y14.5MISO 8015ISO 1101ISO 5459

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Page Information

Last Updated:

2026-07-30

Version:

2.0.0

License:

Free to use for educational and professional purposes.