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Unilateral and bilateral tolerance conversion

Short answer

Unilateral tolerance has variation on one side of basic size (e.g., 25+0.03/0); bilateral on both sides (e.g., 25±0.02). Limits of 40.00±0.03 are 39.97 and 40.03, so unilateral form is 39.97+0.06/0. The dimension 60+0.05+0.02 gives limits 60.02 and 60.05; it is unilateral with tolerance 0.03 mm.

Differentiate between unilateral and bilateral tolerance with examples and state when each is used. Convert the bilateral dimension 40.00±0.0340.00 \pm 0.03 mm into a unilateral form with the same limits, and state the type of tolerance in 60+0.02+0.0560^{+0.05}_{+0.02} mm.

PointUnilateralBilateral
DefinitionTolerance on one side of the basic size onlyTolerance on both sides of the basic size
Example250+0.0325^{+0.03}_{0} or 25−0.02025^{0}_{-0.02}25±0.0225 \pm 0.02 or 25−0.01+0.0325^{+0.03}_{-0.01}
Basic sizeOne of the limitsLies between the limits
UseInterchangeable parts, hole and shaft systems (the basic size is the datum of fits); allows fixed tools to be used and the tolerance to be changed without changing the datumWhere variation on either side is acceptable, e.g. positions of holes, centre distances, and in machining and assembly dimensions
GaugingEasier to adjust setting and to change toleranceSymmetrical; the setting at the mean size

Conversion: the limits of 40.00±0.0340.00 \pm 0.03 are 39.9739.97 and 40.0340.03 mm; the total tolerance is 0.060.06 mm. As a unilateral dimension with the same limits:

39.97 0+0.06 mm39.97^{+0.06}_{\ 0}\ \text{mm}

Type of 60+0.02+0.0560^{+0.05}_{+0.02}: both deviations are positive, so the limits are 60.0260.02 and 60.0560.05 mm and the basic size 60 mm lies outside the tolerance zone. It is a unilateral tolerance (both limits are on the same side of the basic size), with a tolerance of 0.05−0.02=0.030.05 - 0.02 = 0.03 mm.

✓ Answer checked by Claude Opus 5.5 (high effort)

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