May 6, 2009

International Tolerance Grades – ITOl to IT16 – Limits and Fits - Explained

ITOl, ITO, ITl, IT2, IT3, IT4, IT5, IT6, IT7, IT8, IT9, IT10, IT11, IT12, IT13, IT14, IT15, IT16 are the seventeen variations avaliable on International tolerance grades. These variation in part size, also called the magnitude of the tolerance zone, is expressed in grade or IT numbers. Seven grade numbers are used for high-precision parts; these are ITOl, ITO, ITl, IT2, IT3, IT4, IT5.

The most commonly used grade numbers are IT6 through IT16, and these are based
on the Renard R5 geometric series of numbers. For these, the basic equation is


where D is the geometric mean of the size range under consideration and is obtained from the formula

Geometric_MeanThe ranges of basic sizes up to 1000 mm for use in this equation are shown in Table

Size Ranges

With D determined, tolerance grades IT01 through IT16 are found using Eq.and the following table


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