Bonus tolerance is additional geometric tolerance gained when a feature of size departs from its MMC or LMC size, provided the feature control frame uses the appropriate material-condition modifier. It is most often encountered with position tolerance on holes and pins.
When bonus tolerance applies
Bonus tolerance applies only when a material-condition modifier such as MMC or LMC follows the geometric tolerance in the feature control frame. A position tolerance at RFS stays the same at every permitted feature size, so it does not gain bonus tolerance.
How to calculate MMC bonus tolerance for a hole
For a hole, MMC is the smallest permitted diameter. Subtract the hole’s MMC size from its actual measured size. The difference is the bonus tolerance. Add that bonus to the stated geometric tolerance. For a shaft, use the difference between the shaft’s MMC size and its actual measured size.
Keep size and geometry separate
Bonus tolerance does not relax the size limits. The feature must still be within its permitted size range. It also does not erase datum requirements or change the basic location of the feature; it only changes the allowed geometric variation when the applicable modifier is present.
Hole position example
A hole has limits of 10.00–10.20. At 10.00 MMC, the position tolerance is 0.20. At an actual size of 10.12, the hole gains 0.12 bonus tolerance, so the total permitted position tolerance is 0.32. See the complete MMC explanation.
Frequently asked questions
GD&T Bonus Tolerance Explained: How to Calculate MMC and LMC Bonus Tolerance FAQ
What is bonus tolerance in GD&T?
It is extra geometric tolerance gained as a feature of size departs from its MMC or LMC condition, when the applicable modifier is in the feature control frame.
Does MMC always give bonus tolerance?
MMC can provide bonus tolerance on a feature of size when it modifies the geometric tolerance. The drawing must be read carefully because modifiers on datum references have a different meaning.
Does bonus tolerance change the basic dimensions?
No. Basic dimensions still define the exact target. Bonus tolerance changes the size of the allowed geometric tolerance zone.
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GD&T Bonus Tolerance Explained: How to Calculate MMC and LMC Bonus ToleranceCurrent article