Mechanical Engineering - Workshop Technology - Discussion

Thanks @Biren.

Basic shaft : upper deviation zero.

Basic Hole: If the lower limit size or minimum size of the hole is equal to the basic size then that type of hole is known as a basic hole for a given assembly of hole and shaft.

For the basic hole, the zero line will be lying on the minimum size of the hole. For the Basic Hole, the lower deviation is zero because the difference between the Lower Limit Size and Basic Size is zero.