Press-fit tolerances
Check the worst-case hole and shaft limits, distinguish interference from transition fits, and plan material, finish, assembly and inspection for a press-fit joint.
The full size range determines the fit
A press-fit joint uses interference between mating features. A shaft nominally larger than a hole does not guarantee interference once both tolerance ranges are included.
Clearance throughout
Example: D − d = +0.010 to +0.040 mm. The size limits leave positive diametral clearance throughout the range.
Transition is possible
Example: D − d = −0.010 to +0.010 mm. Some size combinations interfere; others have clearance.
Interference throughout
Example: D − d = −0.035 to −0.005 mm. The shaft is larger than the hole throughout the size range.
Illustrative diametral size ranges, not recommended fits. Form, position, texture, temperature and assembly stresses require separate checks.
Here D is hole diameter and d is shaft diameter. Positive D − d means diametral clearance; negative D − d means diametral interference.
Check the smallest and largest interference
Explore a press-fit size stack
Change the example dimensions to see the worst-case diametral size difference. The starting values are an illustration, not a manufacturing capability.
Interference throughout this size range
-0.035 to -0.005 mm diametral size difference
Per-side difference: -0.0175 to -0.0025 mm. Positive means clearance; negative means interference.
Minimum = (D − hole tolerance) − (d + shaft tolerance). Maximum = (D + hole tolerance) − (d − shaft tolerance).
This checks size limits only. Position, form, roughness, temperature, moisture and the final finish can still prevent assembly. Use finished-part limits and validate the actual mating parts.
In this illustrative example, a 10.000 ± 0.010 mm hole has limits of 9.990–10.010 mm. A 10.020 ± 0.005 mm shaft has limits of 10.015–10.025 mm.
Minimum diametral interference = smallest shaft − largest hole = 10.015 − 10.010 = 0.005 mm. Maximum = largest shaft − smallest hole = 10.025 − 9.990 = 0.035 mm. These limits describe size overlap only; they do not establish safe assembly force or joint capacity.
Choose interference for the complete joint
| Input | Why it matters | Review |
|---|---|---|
| Materials and condition | Stiffness, strength, yield behavior and thermal expansion change contact behavior. | Named alloys/conditions and relevant service temperatures. |
| Hub and shaft geometry | A thin hub or hollow shaft responds differently from solid, thick components. | Wall thickness, engagement length, shoulders and local transitions. |
| Loads and life | Retention, torque, vibration, shock and cycling place different demands on the interface. | The actual load cases and required life, including possible fretting. |
| Surface and finish | Texture, coatings, contamination and assembly lubricant affect contact. | Delivered surface requirements and a controlled assembly condition. |
| Serviceability | The joint may need removal without damaging surrounding parts. | Disassembly access, replacement strategy and permitted heating or tooling. |
Bearing seats must follow the bearing maker’s application guidance. A generic pin/hub example does not determine bearing internal clearance or the correct fit for a rotating load.
Use a fit code with its nominal size and standard
A designation such as H7 is a hole tolerance class, not a complete mating fit or a fixed number of micrometers for every diameter.
- Specify both mating features. Identify hole and shaft classes or explicit limits, nominal size, units and the applicable standard. A class on one part cannot define the fit by itself.
- Read the size interval correctly. Limit deviations depend on the nominal-size range in the selected standard. Do not reuse values from a nearby diameter without checking the interval.
- Define geometry as well as size. Cylindricity, straightness, axis alignment and the relevant datum relationships can affect assembly even when two-point sizes are within limits.
- Preserve the governing system. ISO and ASME conventions are not identical. State the drawing standard and edition rather than mixing defaults from separate systems.
Include finish and temperature in the fit decision
| Change | Possible consequence | Release requirement |
|---|---|---|
| Added coating on a shaft | The outside diameter increases on both sides. | Final coated limits or a defined masking/finishing operation. |
| Added coating inside a hole | The bore can become smaller. | Final hole limits and whether the selected process can coat the bore uniformly. |
| Conversion treatment | Total layer thickness may differ from outward growth. | Process-specific growth allowance; do not use full anodize thickness as pure buildup. |
| Different operating temperatures | Differential expansion can increase or reduce interference. | Material, transient and steady operating conditions in the design analysis. |
| Polymer mating component | Moisture, temperature, creep and molding/printing history can change fit. | The exact material, conditioning and long-term validation requirements. |
For bearing assemblies, thermal mounting and fits can alter internal clearance. Follow the specific bearing instructions and temperature limits.
Design the installation path and support
A successful size stack still needs an assembly method. Plan alignment, entry geometry, supporting surfaces and how force reaches the interference interface.
- Provide a controlled entry. Agree lead-in chamfers and edge condition without removing functional engagement. Keep burrs and debris out of the joint.
- Support the right surface. Pressing through a thin unsupported feature can damage it. For rolling bearings, do not transmit installation force through the rolling elements.
- Set the assembly condition. Specify the approved lubricant, cleanliness and any thermal method. These are design/process choices, not interchangeable shop preferences.
- Validate a representative assembly. Check installation behavior, final location and the required retention or performance. Do not infer joint capacity from the force needed to press one sample.
Release limits that can be measured
| Item | Specify |
|---|---|
| Both components | Nominal sizes, limits, units, materials and revisions; identify customer-supplied mating parts. |
| Functional geometry | Engagement, lead-ins, seating shoulder, form and alignment requirements. |
| Surface state | Texture, final finish, masking and inspection before or after treatment. |
| Measurement | Method, locations, temperature/conditioning and required report. |
| Assembly validation | Approved method, any force/displacement recording and the actual acceptance test. |
See surface roughness and machined-parts inspection for the related drawing and evidence requirements.
Frequently asked questions
How much interference should a press fit have?
There is no universal amount. Select it from the materials, nominal diameter, hub/shaft geometry, engagement, loads, temperature, texture and assembly method. Bearing applications need the bearing maker’s fit guidance.
How do I calculate minimum interference?
Subtract the largest permitted hole from the smallest permitted shaft. Maximum interference is the largest shaft minus the smallest hole. Check both limits rather than comparing nominal diameters alone.
Does H7 define a press fit?
No. H7 specifies a hole tolerance class within an applicable size interval and standard. The shaft limits and the hole limits together determine whether the fit is clearance, transition or interference.
Is diametral interference the same as radial interference?
No. For a concentric cylindrical size comparison, the radial difference is half the diametral difference. State the convention whenever reporting an interference value.
Can a fit calculator predict assembly force?
A size-stack calculator alone cannot. Force and joint capacity also depend on geometry, material response, surface condition, friction, alignment and the assembly route.
Should a press-fit diameter be inspected after anodizing?
If the joint functions in the anodized state, define and verify the final limits or an approved masked interface. Anodize growth is not identical to total layer thickness, so the process allowance must be established correctly.
Sources and further reading
- ISO 286-1:2010 — basis of tolerances, deviations and fitsPublic scope for the ISO system of tolerances on linear sizes.
- ISO 286-2:2010 — hole and shaft limit deviationsUse the applicable nominal-size interval and edition; no standards tables are reproduced here.
- SKF — rolling bearing catalogueApplication-specific fit selection, temperature, housing/shaft construction and mounting guidance.
- SKF — bearing damage and failure analysisInstallation force paths and damage mechanisms; bearing-specific guidance is not a generic hub design rule.
Quote the mating interface, not just one diameter.
Upload your CAD and drawing with the material, quantity, finishing and critical dimensions. Confirm the manufacturing route before production.