Calculator Inputs
Formula Used
The calculator uses an ISO style tolerance unit for standard grades:
i = 0.45 × ∛D + 0.001D
Here, D is the nominal diameter in millimeters. The value i is in micrometers.
IT grade tolerance = multiplier × i
Limit sizes are calculated as:
Hole minimum = D + EI / 1000
Hole maximum = D + ES / 1000
Shaft minimum = D + ei / 1000
Shaft maximum = D + es / 1000
The final fit values are:
Minimum clearance = Hole minimum - Shaft maximum - allowance
Maximum clearance = Hole maximum - Shaft minimum - allowance
Positive clearance gives a clearance fit. Negative maximum clearance gives an interference fit. A range crossing zero gives a transition fit.
How to Use This Calculator
- Enter the nominal shaft and hole diameter in millimeters.
- Select the hole letter and grade from the drawing.
- Select the shaft letter and grade from the drawing.
- Add a surface allowance when coating, roughness, or plating matters.
- Add temperature data when assembly and operation temperatures differ.
- Choose manual mode when exact deviations are already specified.
- Press the calculate button to show limits above the form.
- Use the chart, CSV, and PDF options for reporting.
Example Data Table
| Nominal Size | Hole | Shaft | Common Use | Expected Behavior |
|---|---|---|---|---|
| 25 mm | H7 | g6 | Sliding guide | Small positive clearance |
| 40 mm | H7 | h6 | Close running part | Clearance near zero |
| 50 mm | H7 | k6 | Accurate location | Possible transition |
| 80 mm | H7 | p6 | Pressed hub | Probable interference |
Engineering Fits in Machine Design
Why Fits Matter
Engineering fits define how two manufactured parts meet. A shaft may slide, locate, rotate, or press into a hole. The correct fit controls function, wear, noise, heat, assembly force, and service life. A loose fit may cause vibration. A tight fit may cause damage during assembly.
Clearance, Transition, and Interference
A clearance fit always leaves space between the shaft and hole. It is useful for sliding parts, running shafts, bushings, and removable assemblies. A transition fit may create either small clearance or small interference. It is common for accurate location where movement should be limited. An interference fit makes the shaft larger than the hole. It is used for pressed gears, collars, pulleys, bearing seats, and permanent joints.
Using Limits Instead of Single Sizes
Real parts are never made to one perfect size. Every part has a permitted range. The hole has a lower and upper limit. The shaft also has a lower and upper limit. The worst case clearance is found by comparing the smallest hole with the largest shaft. The largest clearance is found by comparing the largest hole with the smallest shaft.
Practical Design Review
This calculator helps designers check fit behavior before production. It estimates tolerance zones, limit sizes, clearance range, temperature effects, and assembly sensitivity. It also accepts manual deviations, so it can follow exact drawing values or supplier tables. Use the results during design review, drawing checks, inspection planning, and shop discussions.
Important Note
Standard tables should be used for final drawings. This tool is best for planning, comparison, education, and quick verification. Always confirm critical aerospace, medical, pressure, or safety parts with the governing standard and a qualified engineer.
FAQs
1. What is an engineering fit?
An engineering fit describes the size relationship between a hole and a shaft. It shows whether the parts will slide freely, locate closely, or press together.
2. What is a clearance fit?
A clearance fit means the smallest hole is still larger than the largest shaft. The parts can assemble without pressing force.
3. What is an interference fit?
An interference fit means the shaft is larger than the hole in all limit conditions. Assembly usually needs force, heat, cooling, or special tooling.
4. What is a transition fit?
A transition fit can produce either clearance or interference. It is useful when accurate location matters and movement must remain limited.
5. What does H7 mean?
H7 is a hole tolerance designation. H defines the tolerance zone position. 7 defines the tolerance grade size.
6. Why are deviations shown in micrometers?
Fits often use very small differences. Micrometers make small tolerance values easier to read, compare, and document accurately.
7. Should I use manual mode?
Use manual mode when your drawing, supplier, or standard table gives exact EI, ES, ei, and es values.
8. Can temperature change the fit?
Yes. Different materials expand at different rates. Temperature can reduce clearance, increase clearance, or change assembly behavior.