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International Tolerance (IT) Grades reference ISO 286. This mechanical tolerance grade specifies tolerances with associated manufacturing processes for a given dimension.
International Tolerance grades are calculated as following:
Where:
T = Tolerance in micrometers [µm]
D = Geometric mean dimension in millimeters [mm]
ITG = IT Grade, a positive integer.
Application:
Most manufacturing processes have an IT Grade designated for specification. IT grades provide guidance for typical manufacturing process capability or how precise one can except manufacture of a particular features or features.
When designing a part and specifying mechanical tolerances, engineering or design will determine size and location for a particular feature. Using the designated International Tolerance Grade formula, the IT Grade required or typical to produce the part feature is assigned. For example, plastic injection molding is determined to have an IT Grade of 13 and a part needs an IT Grade of 5, engineering and design should consider an alternative and more capable manufacturing process to produce the part and feature.
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