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The IT grade defines the magnitude or size of the tolerance zone—essentially, how much variation is allowed. There are 20 IT grades defined in ISO 286 (IT01, IT0, and IT1 through IT18).
This part establishes the foundational concepts, terminology, and principles for the tolerance code system. It explains:
: While primarily used for cylindrical features (shafts and holes), the standard's principles also apply to non-circular sections, such as the width of a slot or the thickness of a key. Available PDF Resources iso 286 pdf
The standard is the internationally recognized system for limits and fits in mechanical engineering. It provides a standardized framework for defining tolerances on linear sizes, primarily for cylindrical features like holes and shafts , ensuring that mating parts from different manufacturers can be assembled interchangeably. Structure of the ISO 286 Standard
: There is always a gap (e.g., a spinning axle in a bicycle). The shaft is always smaller than the hole. The IT grade defines the magnitude or size
Broader tolerances, used for general machining and non-mating parts. 3. Fundamental Deviations (Letters)
For precise engineering, ensure you are utilizing the most recent version of the ISO 286-1 and ISO 286-2 standards, as revisions can occur to align with modern manufacturing techniques. Share public link It explains: : While primarily used for cylindrical
The standard implements 20 grades of accuracy, known as IT (International Tolerance) grades, to satisfy the diverse requirements of different industries. These are designated from , IT0 , IT1 , IT2 , all the way to IT18 (for sizes up to 500 mm) and IT1 to IT18 for sizes up to 3150 mm.
Used to produce interference (press fits). 🔩 The Three Types of Fits
: Positive allowance — the minimum clearance is greater than zero.
Indicates the fundamental deviation (the position of the tolerance zone).