What is the dimensional tolerance?

Dimensional toleranceThe term "tolerance" refers to the allowable value of the absolute value of the difference between the maximum limit size and the minimum limit size, or the difference between the allowable upper deviation and the deviation. The dimensional tolerance is an absolute value without a symbol. Limit deviation = limit size - basic size, upper deviation = maximum limit size - basic size, lower deviation = minimum limit size - basic size. Dimensional tolerance is the amount of variation allowed for the part size during machining. In the case of the same basic dimensions, the smaller the dimensional tolerance, the higher the dimensional accuracy.

Dimensional tolerance means that there is always a certain error in the actual size after completion due to factors such as machining or measurement during the manufacturing process of the part. In order to ensure the interchangeability of the parts, the actual size of the parts must be controlled within the allowable range of variation. This allowed amount of dimensional variation is called the dimensional tolerance.
example:
1, the basic size design given size: 30mm
2, the limit size allows two limits of size changes:
Maximum limit size = 30 + 0.01 = 30.01mm
Minimum limit size = 30-0.01 = 29.99mm
3, limit deviation The minimum value obtained by subtracting the basic size from the basic size. That is, the algebraic difference obtained from the maximum limit size and the minimum limit size minus the basic size is the upper deviation and the lower deviation, respectively, collectively referred to as the limit deviation. The upper and lower deviations of the holes are indicated by capital letters ES and EI, respectively:
Upper deviation ES=30.01-30=+0.01
Lower deviation EI=29.99-30=-0.01
4, dimensional tolerance: allow the size of the variation, that is, the maximum limit size minus the minimum limit size, is also equal to the algebraic difference obtained by the upper deviation minus the deviation. The dimensional tolerance is an absolute value without a symbol.
Tolerance: 30.01-29.99=0.02
Or I0.01-(-0.01)=0.02