A. Deviation of spiral steel pipe: In the production process, because the actual size is difficult to meet the nominal size requirement, that is, it is often larger or smaller than the nominal size, so the standard stipulates that there is a difference between the actual size and the nominal size. A positive difference is called a positive deviation, and a negative difference is called a negative deviation.
The deviation is directional, that is, it is expressed as "positive" or "negative"; the tolerance is not directional, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".
