Tolerance level refers to the level that determines the degree of dimensional accuracy. The national standard stipulates that it is divided into 20 levels. The larger the number, the lower the tolerance level (processing accuracy), the larger the allowable variation range (tolerance value) of the size, and the less difficult the processing.
On the premise of meeting the usage requirements, a lower tolerance level should be selected as much as possible to reduce processing costs.
For the application range of tolerance levels, please refer to table 1. For the tolerance levels that can be achieved by various processing methods, please refer to table 2. For the selection and application of tolerance levels, please refer to table 3. In addition, surface roughness requirements should also be considered when selecting tolerance levels.
For the fit with the basic size ≤ 500mm, when the tolerance level is higher than or equal to IT8, it is recommended to choose the hole tolerance level one level lower than the shaft; for the fit with the tolerance level lower than IT8 or the basic size > 500mm, it is recommended to choose the hole and shaft fit of the same level.
Table 1 Application range of tolerance classes
Table 2 Tolerance levels achievable by various processing methods
Table 3 Selection and Application of Tolerance Levels
Source: Mechanical Engineer
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