Introduction of nominal size and sctual size of seamless steel pipe:
A. Nominal size: It is the nominal size specified in the standard, the ideal size expected by users and manufacturers, and the order size indicated in the contract.
B. Actual size: It is the actual size obtained in the production process, which is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.
Deviation: In the production process, because the actual size is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, so the standard specifies the allowable difference between the actual size and the nominal size. If the difference is positive, it is called positive deviation, and if the difference is negative, it is called negative deviation.
Tolerance: The sum of the absolute values of the positive and negative deviations specified in the standard is called the tolerance, also known as the "tolerance zone".
Deviation is directional, that is, expressed as "positive" or "negative"; tolerance is not directional, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".