### Standards of limits and fits for mating parts

**METRIC STANDARDS FOR LIMITS & FITS**

**Definitions**

1. Basic size is the size to which limits or deviations are assigned and is the same for both members of a fit. It is measured in millimeters.

2. Deviation is the algebraic difference between a size and the corresponding basic size.

3. Upper deviation is the algebraic difference between the maximum limit and the corresponding basic size.

4. Lower deviation is the algebraic difference between the minimum limit and the corresponding basic size.

5. Fundamental deviation is either the upper or the lower deviation, depending on which is closest to the basic size.

6. Tolerance is the difference between the maximum and minimum size limits of a part.

7. International tolerance grade (IT) is a group of tolerances which have the same relative level of accuracy but which vary depending on the basic size.

8. Hole basis represents a system of fits corresponding to a basic hole size.

9. Shaft basis represents a system of fits corresponding to a basi…