Fit calculator
With the fit calculator from Spanflug, you can quickly and easily calculate the ideal tolerances and fits for your parts. The fit calculator is based on ISO 286, the international standard for tolerances and fits. Our fit calculator allows you to search for specific fit types, dimensions or tolerances and get quick results.
Fits
For the manufacturing of CNC parts, the specification of the correct fits is very important. Fits describe the geometric relationship between two parts that fit together, for example a shaft and a bore. They determine how these parts interact with each other – whether they should move freely, fit exactly or be firmly connected.
Nominal dimension
The nominal dimension of a fit refers to the intended dimension of a part as specified in the technical drawings or design plans. It serves as a reference point for tolerances and fits, the actual dimensions of the part deviate from the theoretical nominal dimension depending on the fit selected.
Tolerance degree
A tolerance degree is a value in manufacturing and design that defines the permissible deviation of a real dimension from the idealized nominal dimension. The range is represented by the numbers 1–18. These numbers indicate the size of the tolerance zone, where 1 represents the narrowest and 18 the largest tolerance zone.
Tolerance position
The tolerance position describes the position of the tolerance zone relative to the zero line. Tolerance positions are identified by letters from A to ZC. The letters A to Z refer to bores. The lower case letters a to zc refer to shafts. For bores, the tolerance zone moves above the zero line as the letter increases, while for shafts the tolerance zone moves below the zero line as the letter increases. The most common tolerance zone is H or h, where the lower or upper value of the tolerance zone lies exactly on the zero line.
Types of fits
Fits are critical in manufacturing and design because they define the functional relationships between mating parts. Fits enable engineers and designers to optimize the performance and service life of machinery and equipment.
Interference fit
An interference fit, also called a press fit, is a type of fit where the bore is smaller than the shaft that is pressed into it. This means the parts are brought together using pressure, for example.
Transition fit
In the transition fit, the tolerances of the shaft and bore are designed so that the diameter of the shaft is either slightly larger or smaller than the inner diameter of the bore. This ensures that the bore and shaft can be joined under light pressure.
Clearance fit
In a clearance fit, the inner diameter of the bore is always larger than the outer diameter of the shaft. This allows the mating parts to move.