AtlasCalcsUtility Calculation Suite
2026-07-30 8 min

Transition Fit Calculator

Calculate transition fit parameters per ISO 286. Compute max clearance, max interference, and probability of clearance for H7/js6, H7/k6, H7/m6, H7/n6 fits.

Calculator

Unit System
Nominal Diameter (mm)
Hole Tolerance
Shaft Tolerance

Results

Optimal

Max Clearance

31.7845mm

Largest possible gap when parts are at LMC

Max Interference

23.1886mm

Largest possible interference when parts are at MMC

Tolerance Spread

54.9731mm

Total range from max clearance to max interference

Prob. of Clearance

57.8183%

Approximate probability of getting clearance (vs interference)

Fit Type

Transition

Fit classification based on tolerance zone overlap

Visualizations

Results Overview

31.8mmMax Clearance
23.2mmMax Interference
55mmTolerance Spread
57.8mmProb. of Clearance

Formula

Transition fit analysis per ISO 286-1:2010. Transition fits have overlapping tolerance zones where either clearance or interference can occur depending on actual part sizes.

Max_Clearance = Hole_Upper - Shaft_Lower, Max_Interference = Shaft_Upper - Hole_Lower

Alternative Form

P(Clearance) = Max_Clearance / (Max_Clearance + Max_Interference) × 100%

Variables

SymbolNameUnitDescription
C_maxMax ClearancemmMaximum possible clearance (at LMC)
I_maxMax InterferencemmMaximum possible interference (at MMC)
P_clearClearance Probability%Estimated probability of clearance fit
T_spanTolerance SpreadmmSum of max clearance and max interference

Explanation

Transition fits are used when some positional accuracy is needed but assembly/disassembly should still be possible. The actual outcome (clearance or interference) depends on the random combination of hole and shaft sizes within their tolerance zones.

Derivation

The probability of clearance is approximated by the ratio of the clearance zone to the total tolerance spread, assuming uniform distribution of part sizes within tolerance zones. In reality, manufacturing processes often produce normal distributions centered within the tolerance band.

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 (H7 recommended).

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

Select shaft tolerance for transition (js6, k6, m6, n6).

Shaft:k6
Result: Shaft zone: 1.7357/23.1886 mm
Step 3

Evaluate transition fit characteristics.

P(Clearance) = C_max / (C_max + I_max)
Max Clearance:31.7845 mm
Max Interference:23.1886 mm
Intermediate: P(Clearance) = 31.7845 / 54.9731
Result: Fit: Transition, 57.8183% chance of clearance
Final Answer
31.7845

Worked Examples

See how the calculator works with different scenarios.

Scenario

A precision transition fit for a gear on a shaft where light hand assembly is needed but some positional accuracy is required.

Inputs

Nominal Diameter:25 mm
Hole:H7
Shaft:k6

Calculation

H7: 0/+21 µm k6: +2/+15 µm (approx) Max Clearance = 21 - 2 = 19 µm Max Interference = 15 - 0 = 15 µm P(Clearance) = 19/(19+15) = 56%

Result

Transition fit: max clearance 19 µm, max interference 15 µm, 56% clearance probability

Interpretation

H7/k6 provides a nearly balanced transition fit commonly used for gears and pulleys that need occasional removal.

Understanding Your Result

Your Result: Max Clearance: 31.7845 mm

Typical range: H7/js6: 84% clearance / 16% interference. H7/k6: 56% clearance / 44% interference. H7/m6: 43% clearance / 57% interference. H7/n6: 31% clearance / 69% interference.

What This Means

A transition fit is an intermediate fit where the assembled parts may have either clearance or interference, depending on the actual manufactured sizes within their tolerance zones.

Why It Matters

Transition fits are used when positional accuracy is needed but assembly/disassembly by hand or light tools should still be possible. They bridge the gap between clearance fits (for motion) and interference fits (for permanent assembly).

Professional Interpretation

Transition fits are statistical fits - the actual result depends on the manufacturing distribution. A process centered in the tolerance band will produce a mix of clearance and interference fits. Designers should consider the functional impact of both outcomes.

Recommendations

  • •Use H7/k6 for the most balanced transition fit with equal probability of clearance or interference
  • •Use H7/m6 when some interference is preferred but hand assembly is still desired
  • •Use H7/n6 when tight positioning is critical and assembly with light hammer taps is acceptable
  • •Use H7/js6 for applications where disassembly frequency is high and clearance is preferred
  • •Combine transition fits with keys or pins for torque transmission
  • •Consider statistical process capability when designing transition fits
  • •Verify that both clearance and interference outcomes are acceptable for the function

Educational Content

Introduction

A transition fit is a fit where the tolerance zones of the hole and shaft overlap. Depending on the actual sizes, the assembly may have either a small clearance or a small interference.

Concept Explanation

Transition fits provide a compromise between the free movement of clearance fits and the rigidity of interference fits. They are used when parts need accurate location but may need to be disassembled occasionally.

Applications

▸Gears on shafts (with key for torque)
▸Bearing mounting on shafts
▸Dowel pins and alignment pins
▸Clutch hubs
▸Pulley or sprocket mounting
▸Coupling halves
▸Machine tool spindle assemblies

Benefits

  • •Provides good centering accuracy
  • •Allows assembly/disassembly without heavy equipment
  • •Suitable for parts requiring occasional replacement
  • •Better concentricity than clearance fits
  • •Reduces fretting compared to loose fits

Limitations

  • •Cannot guarantee either clearance or interference
  • •May require selective assembly for critical applications
  • •Less suitable for high torque without additional fasteners
  • •Assembly force varies significantly with actual sizes

Best Practices

  • •Use in combination with keys, splines, or set screws for torque transmission
  • •Specify both clearance and interference as acceptable outcomes
  • •For critical applications, add a note for selective assembly
  • •Consider that surface finish affects the effective fit outcome
  • •Document the probability expectation on engineering drawings
  • •Use statistical process control to maintain desired fit distribution

Common Misconceptions

Myth: Transition fits always give a slight interference.
Truth: Many transition fits (like H7/js6) give clearance more often than interference. The distribution depends on the specific grade combination.
Myth: Transition fits are not reliable for positioning.
Truth: Despite the overlap, the actual clearance or interference is small (typically < 0.05 mm), providing good positioning accuracy.
Myth: Any fit with H and k through n is a transition fit.
Truth: H7/n6 approaches light interference and may act as an interference fit for most process distributions.

Practical Tips

  • •For assemblies requiring consistent fit behavior, consider selective sorting by actual size
  • •Transition fits work best when manufacturing processes are centered and capable (Cpk > 1.33)
  • •For temperature-sensitive applications, verify fit at operating temperature
  • •Use surface finish of Ra ≤ 1.6 µm to avoid roughness affecting the fit classification
  • •On drawings, note "Transition Fit" alongside the tolerance specification to alert production
  • •Consider adding a keyway or set screw as a safety measure if fit becomes clearance
  • •For high-volume production, analyze actual size distribution to verify fit probability matches expectations

Common Mistakes

Selecting transition fit for high-torque applications without additional torque transmission features
Always combine transition fits with keys, splines, or pins when significant torque must be transmitted.
Assuming transition fit always gives interference
Check the fit classification: if max clearance > 0, clearance is possible. Use the probability calculation to understand the distribution.
Using transition fit for parts requiring frequent disassembly
If disassembly is frequent, H7/js6 is preferred. For very frequent disassembly, consider a clearance fit with a positioning feature.
Not accounting for coating thickness in transition fits
Plating, painting, or anodizing layers change the effective fit. Specify tolerances for the final (coated) condition.

Assumptions

This calculator makes the following assumptions to provide estimates:

Uniform Size Distribution: Probability calculation assumes uniform distribution of sizes within tolerance zones. Actual manufacturing distributions are often normal.
Room Temperature: All dimensions referenced to 20°C. Temperature differences change actual clearances and interferences.
No Elastic Deformation: Deformation due to assembly forces is not considered. Light interferences may become clearance after elastic recovery.
Circular Parts: Assumes perfectly round holes and shafts. Form errors affect fit classification.

Limitations

Be aware of these limitations when using this calculator:

Approximated Deviations: Shaft deviations for js, k, m, n are approximated. Exact ISO 286 tables should be used for critical designs.
Simplified Probability: Clearance probability assumes uniform distribution. Actual probability depends on process capability and centering.
Limited Hole Options: Only H7 hole is provided. Other hole grades (H6, H8) may also be used for transition fits in specialized applications.
No Stress Calculation: When interference occurs, resulting stress is not calculated. Use interference fit calculator for detailed stress analysis.

Frequently Asked Questions

Answers to common questions about this calculator.

What is a transition fit?
A transition fit is a fit where the tolerance zones of the hole and shaft overlap, meaning the assembly may have clearance or interference depending on the actual part sizes.
What does H7/k6 mean?
H7/k6 is an ISO 286 transition fit. H7 hole (0 to +21 µm) and k6 shaft (+2 to +15 µm approximately). The zones overlap, giving a 56% chance of clearance for 25 mm size.
How is transition fit probability calculated?
Probability of clearance = Max Clearance / (Max Clearance + Max Interference) × 100%. This assumes uniform distribution of sizes within the tolerance zones.
What shaft grades give transition fits with H7?
js6, k6, m6, and n6 produce transition fits with H7. js6 favors clearance, k6 is balanced, m6 favors interference, n6 approaches light press fit.
What is the difference between H7/k6 and H7/m6?
H7/k6 is a balanced transition (56% clearance, 44% interference). H7/m6 favors interference (43% clearance, 57% interference). m6 has higher shaft deviation.
When should I use a transition fit?
Use transition fits when you need accurate part location but still want to be able to assemble/disassemble by hand or with light tools.
Can transition fits transmit torque?
Only light torque. Always use keys, splines, or set screws for torque transmission in transition fits.
How is H7/js6 different from other transition fits?
H7/js6 uses a symmetrical shaft tolerance (js = ±IT/2). It gives the highest probability of clearance (84%) among standard transition fits.
What is the typical clearance range for H7/k6?
For 25 mm H7/k6: max clearance ≈ 19 µm, max interference ≈ 15 µm. Actual values depend on nominal size.
How do I specify transition fit on a drawing?
Use ISO notation: ø25 H7/k6. You can also add a note: "Transition Fit - Hand Assembly".
Is H7/n6 still a transition fit?
Technically yes, but it behaves mostly as a light press fit with 69% interference probability. Some standards classify it as a light press fit.
How does manufacturing capability affect transition fits?
If the process is not centered, actual probabilities differ from calculations. Example: if hole sizes trend high, clearance probability increases.
What is the advantage of transition over interference fits?
Transition fits allow disassembly without special equipment and reduce the risk of hub yielding compared to interference fits.
Can surface treatment change a transition fit?
Yes. Coatings of 5-15 µm (plating, anodizing) can shift a balanced transition fit to consistently clearance or consistently interference.
What if I need guaranteed clearance but good centering?
Use a close clearance fit (H7/g6) with close tolerances. The clearance is small and consistent while still guaranteeing no interference.
What if I need guaranteed interference but light assembly?
Consider a light press fit (H7/p6) which guarantees interference but with minimal interference for press assembly.
What is selective assembly for transition fits?
Parts are sorted by actual size and matched to achieve desired fit outcomes. For example, larger holes paired with larger shafts to favor interference.
How does temperature affect transition fits?
Temperature changes alter actual sizes. If the assembly operates at a different temperature than assembly, the fit classification may shift.
What is the maximum interference for a transition fit?
For H7/n6 at 100 mm: max interference ≈ 33 µm. For H7/m6 at 100 mm: max interference ≈ 24 µm.
Can transition fits be used for bearings?
Yes. Many bearing-to-shaft fits are transition fits (k6, m6). Bearings on rotating shafts typically use k6 or m6.
How do I calculate assembly force for transition fits?
When interference occurs, assembly force depends on the actual interference. Use the most likely interference value for planning.
What is the ISO standard for transition fits?
ISO 286-1 and ISO 286-2 define the tolerance zones and deviations for transition fits. ISO 2768 provides general tolerances.
How does wear affect transition fits over time?
Wear increases clearance. A transition fit that starts with interference may become clearance over the life of the product.
What are common applications for H7/k6?
Gears on shafts, bearing inner rings, pulleys, sprockets, clutches, and general machine tool spindles.
Can I use transition fit with aluminum parts?
Yes, but aluminum's higher thermal expansion means more thermal sensitivity. Consider differential expansion in design.
What is the difference between symmetric (js) and asymmetric (k, m, n) deviations?
js is centered on the nominal (bilateral). k, m, n are shifted positive (above nominal) giving progressively more interference.
How do lubrication holes affect transition fits?
Lubrication holes in the shaft reduce effective contact area marginally but do not significantly affect fit behavior.
What is the cost implication of transition fits?
Transition fits require reasonable manufacturing control (IT6-IT7). Costs are moderate - less than precision fits (IT5+) but more than general tolerances (IT9+).
Can transition fits be used in aerospace?
Yes, with strict traceability and often with selective assembly. Aerospace applications frequently use transition fits for shaft-mounted components.
How does part geometry affect transition fits?
Thin-walled parts may deform elastically during assembly, changing the effective fit. Account for wall thickness in the design.
What is the reliability of transition fit probability calculation?
The probability calculation is approximate. For critical applications, perform a Monte Carlo simulation using actual process capability data.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

Bilateral Tolerance
A tolerance that extends equally in both positive and negative directions from the nominal (e.g., js = ±IT/2).
Clearance Probability
The estimated likelihood that a random assembly will result in clearance rather than interference.
Fit Distribution
The statistical distribution of clearance or interference outcomes for a population of assemblies.
Interference Probability
The estimated likelihood that a random assembly will result in interference rather than clearance.
Overlapping Zones
The characteristic of transition fits where hole and shaft tolerance zones share common size ranges.
Selective Assembly
A manufacturing process where parts are measured and selectively matched to achieve desired fit outcomes.
Symmetric Deviation
A fundamental deviation where the tolerance zone is centered on the nominal size (js only).
Tolerance Overlap
The region where hole and shaft tolerance zones coincide, causing the fit to be indeterminate.
Tolerance Spread
The total range from maximum clearance to maximum interference in a transition fit.
Transition Fit
A fit where the tolerance zones of hole and shaft overlap, producing either clearance or interference.
Uniform Distribution
An assumption that part sizes are equally likely anywhere within the tolerance zone.
Zone Overlap Ratio
The measure of how much the tolerance zones overlap, expressed as a percentage.

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.