May 24, 2018

**1. Size deviation (deviation)**

Size deviation is a certain size minus its nominal size to get the algebraic difference, it can be divided into actual deviation and extreme deviation.

(1) The actual deviation. The actual size minus its nominal size is called the actual deviation. The actual deviation is represented by "Ea" or "ea".

(2) Limit deviation. The algebraic difference used the limit size minus its nominal size is called the limit deviation. The limit deviation divided into the upper limit deviation and the lower limit deviation. The upper limit deviation is the algebraic difference between the upper limit size minus the nominal size, and the lower limit deviation is the algebraic difference between the lower limit size minus the nominal size. The deviation value is a substitute value, which can be positive, negative or zero. The upper limit deviations of the hole and the axis are respectively "ES" or "es" , and the lower limit deviations of the hole and the axis are respectively "EI" and "ei".

**2. Basic deviation**

In the national limit and fit standard, the upper limit deviation or lower limit deviation closest to the zero line is called the basic deviation, which is used to determine the deviation between the tolerance and the relative position of the zero line.

**3. Dimensional tolerance**

Dimensional tolerance. Dimension tolerance is the allowable change in size. The dimensional tolerance is equal to the absolute value of the algebraic difference between the upper limit and the lower limit, which is also equal to the absolute value of the algebraic difference between the upper limit deviation and the lower limit deviation. Tolerance is absolute value, cannot be negative, cannot be zero (tolerance is zero, parts will not be processed). The tolerance of holes and axes is represented by "Th" and "Ts" respectively.

**4. Standard tolerance**

The tolerance value specified in the national standard to determine the size of tolerance is the standard tolerance.

**5. Tolerance zone**

In the tolerance band diagram, a region defined by two lines representing the upper limit deviation and the lower limit deviation or the upper limit size and the lower limit size. It is determined by the tolerance size and the position of its relative zero line, such as the basic deviation

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