What is Limit System and important Terms used in Limit System?

In mechanical engineering System of limits or Limit System is a concept of controlling the sizes of machine elements while manufacturing each component. Because taking exact dimensions is an ideal condition but in practical(Manufacturing/Measuring) methods, it is not possible. So limit system enables how much amount of deviation is acceptable. How do we apply the limit system in the design of the machine elements? When one part is matting with another one, first of all, the fit between the two parts must be determined. [Learn more about Types of Fits]. To determine the fit, we must take one component as the constant member and the second component will have the deviations according to the type of fit chosen. By making a constant member we can classify them as hole basis system and shaft basis system. these are the two bases of the limit system. In hole basis system Hole values are constant and the deviations will be considered in the shaft dimensions. In Shaft basis system the shaft dimensions are constant and the deviation will be considered in the hole dimensions. Let’s back to the subject, so what are the important nomenclature used in the limit system? Important Terms Used in Limit System Nominal size Basic size Actual size Limits of sizes Tolerance Allowance Tolerance zone Zero line Upper deviation