Dimension and Tolerance terms

The following terms are used generally in dimensioning:

• Nominal size. The size we use in speaking of an element. For example, we may

• Limits. The stated maximum and minimum dimensions.

• Tolerance. The difference between the two limits.

• Bilateral tolerance. The variation in both directions from the basic dimension. That is, the basic size is between the two limits, for example, 1.005 ± 0.002 in. The two parts of the tolerance need not be equal.

• Unilateral tolerance. The basic dimension is taken as one of the limits, and variation is permitted in only one direction, for example,1.005 +0.004 ?0.000 in

• Clearance. A general term that refers to the mating of cylindrical parts such as a bolt and a hole. The word clearance is used only when the internal member is smaller than the external member. Thediametral clearance is the measured difference in the two diameters. The radial clearance is the difference in the two radii.

• Interference. The opposite of clearance, for mating cylindrical parts in which the

internal member is larger than the external member.

• Allowance. The minimum stated clearance or the maximum stated interference for mating parts.

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