Fits and Tolerances Calculator
Calculate ISO 286 limits and fits for hole and shaft pairings.
| Parameter | Hole (mm) | Shaft (mm) |
|---|---|---|
| Upper Limit | - | - |
| Lower Limit | - | - |
| Tolerance Zone | - | - |
Understanding Fits and Tolerances
In precision engineering and manufacturing, fits and tolerances define the allowable deviation from a nominal dimension to ensure parts function correctly when assembled. The ISO 286 System of Limits and Fits is the international standard used to specify these tolerances for cylindrical parts (holes and shafts).
A Fit represents the relationship between two mating parts. Depending on the size difference between the hole and the shaft, the fit can allow for free rotation, require a light press, or ensure a permanent stationary connection.
Types of Engineering Fits
Our calculator helps you identify three primary categories of fits:
- Clearance Fit: The shaft is always smaller than the hole. This ensures there is always a gap (clearance) for movement or lubrication. Common examples include H7/g6 or H8/f7.
- Interference Fit: The shaft is larger than the hole. Assembly usually requires force, heat, or cold. These are used for permanent assemblies where no relative movement is desired (e.g., H7/p6).
- Transition Fit: Depending on the actual manufactured sizes within the tolerance range, the fit might result in either a small clearance or a small interference. Used for precise positioning (e.g., H7/k6).
How to Use the Fits Calculator
To use this tool, follow these simple steps:
- Enter the Nominal Size of the mating parts in millimeters.
- Select the Hole Tolerance Class (e.g., H7 is a very common standard).
- Select the Shaft Tolerance Class (e.g., g6 for a sliding fit).
- Click "Calculate Limits" to view the upper and lower manufacturing limits, the total tolerance, and the resulting fit type.
Frequently Asked Questions
Q: What does H7 mean?
A: 'H' stands for the fundamental deviation (position of the tolerance zone relative to the zero line), and '7' is the IT grade (International Tolerance), which defines the width of the tolerance zone.
Q: Why is the Hole-Basis system common?
A: Most manufacturers prefer the Hole-Basis system (keeping the hole size constant and varying the shaft) because holes are typically made with standard-sized drills or reamers, which are harder to adjust than shafts turned on a lathe.