A2.1 DEFINITIONS

In the metric system, several terms are used to describe features of dimensional relationships between mating parts:

Dimensional tolerance. Dimensional tolerance is defined as the permissible or acceptable variation in the dimensions of a part.

Nominal size. The dimension that is used for the purpose of general identification. It is written into drawings and other technical documentation.

True size. The dimension that is measured on a finished part. Like all other sizes, this size includes inaccuracy of measuring.

Limit sizes. Limit sizes are two given sizes, between which must be the true size of a correct piece.

Upper limit size. Upper limit size is the maximum allowance for the dimension of a correctly made piece.

Lower limit size. Lower limit size is the minimum allowance dimension of a correctly made piece.

Maximum material condition. A piece whose dimensions are at the upper limit size.

Minimum material condition. A piece whose dimensions are at the lower limit size.

Deviation. Algebraic difference between some certain size and nominal size. The value is positive if this size is larger than nominal size and negative if it is less than nominal size.

Zero line. A straight line that, in a graphical interpretation of tolerance, corresponds with nominal size, so it is the beginning line for the calculation of deviations.

Upper deviation. Algebraic difference between upper limit size and nominal size.

Lower deviation. Algebraic difference between lower limit size and nominal...