Definition
Position is a geometric tolerance that controls how far the true location of a feature, commonly a hole, may deviate from its theoretically exact location, defined by basic dimensions.
What it means for the calculation
Position tolerance on a hole pattern often drives the fixturing and drilling sequence, sometimes a jig-boring or CMM-verified operation. Tight positions on many holes usually raise cost more than a single tight diameter would.
Where it appears on the drawing
In a feature control frame with the ⌖ symbol, a tolerance value (sometimes prefixed with a diameter symbol for a cylindrical zone), and one or more datum references.
Common mistakes
Measuring from an edge instead of the specified datum structure. Also forgetting that position tolerance defines a cylindrical (or other shaped) zone, not a simple ± offset in one direction.
Position tolerance on a hole pattern often drives the fixturing and drilling sequence, sometimes a jig-boring or CMM-verified operation. Tight positions on many holes usually raise cost more than a single tight diameter would.
See how Blake reviews a partFrequently asked questions
Why use position instead of two separate ± dimensions for a hole?
Because position defines a single round tolerance zone, which better matches how a hole actually varies and often allows a larger usable zone than two separate ± dimensions.
What is a basic dimension in this context?
The theoretically exact location the hole is measured against; it carries no tolerance of its own.
Can position tolerance change with the actual size of the hole?
Yes, if the drawing invokes a material condition modifier (MMC/LMC), the allowed position tolerance can grow as the hole's actual size departs from its worst-case limit (bonus tolerance).