Algebraic difference between a size and a corresponding basic size is called deviation. Limit deviations are upper and lower deviations. Algebraic difference of actual size with basic size is called actual deviation.
Upper Deviation: It is the algebraic difference between the maximum size and the basic size.
The upper deviation of a hole is represented by a symbol ES (Ecart Superior) and of a shaft, it is represented by es.
Lower Deviation: It is the algebraic difference between the minimum size and the basic size. The lower deviation of a hole is represented by a symbol EI (Ecart Inferior) and of a shaft, it is represented by ei.

Blast furnace is used to produce Pig iron

Interference Fit Interference fit is defined as the fit established when a negative clearance exists between the sizes of the holes and the shaft. In Interference fit, the minimum permitted diameter of the shaft is larger than the maximum allowable diameter of the hole.

Examples for Interference Fit are: Bearing bushes, small end in the connecting rod.