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What does a position tolerance of zero at MMC mean?

Last updated 10 August 2026

It means a hole exactly at maximum material condition gets no position tolerance at all, and every thousandth it grows past that becomes position tolerance it can use.

It looks like a mistake and it is not. At MMC the hole is at its smallest, the fastener needs all of it, and there is nothing left over to allow the hole to be out of position. Open the hole and the slack that appears is real, so the standard lets you spend it on location.

The reason to write it this way rather than to state a small tolerance is that it accepts more good parts. A hole near the top of its size range gets more position tolerance under zero at MMC than it would under a fixed .005, and a hole at the bottom gets exactly what it can afford. What it costs is that nobody can check position without knowing the actual size, so a coordinate readout on its own is no longer an answer.

Worked

The frame⌖|⌀0Ⓜ|A
ControlPosition
FamilyLocation control
Datum referencerequired
Diametral zoneallowed
Material condition modifierallowed
Legal under ASME Y14.5-2018yes

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Computed by ctrlPlanner. ASME Y14.5-2018.

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