Perpendicularity is a GD&T orientation control that keeps a surface, axis or centre plane at exactly 90° to a datum. For a surface the zone is two parallel planes square to the datum; for a hole or pin axis it is usually a cylinder, and it can take MMC for bonus tolerance.
On a face, perpendicularity is squareness: the face must fit between two parallel planes that are at 90° to datum A and the tolerance apart. It also limits the flatness of the face.
On a hole or pin, the frame sits under the diameter dimension and controls the axis. The zone is a cylinder, perpendicular to the datum, as long as the feature. This is how you make sure a dowel pin stands square or a bore lines up with a bearing face.
Perpendicularity does not locate anything. A square hole can still be in the wrong place; position controls that, and a position tolerance referencing the same primary datum also controls perpendicularity within its value.
For a surface: two parallel planes at 90° to the datum, the tolerance value apart. For an axis with a diameter symbol: a cylinder of that diameter, at 90° to the datum, the length of the feature.
The zone may move sideways to suit the part, since only orientation is controlled.
Perpendicularity always needs a datum, usually a flat face. A second datum is added when the direction of tilt matters, for example a face that must be square to both a base and a side.
| Modifier | With perpendicularity |
|---|---|
| MMC or LMC | Allowed when applied to a feature of size (hole, pin, slot). The tolerance grows by the departure from that material condition. |
| Zero at MMC | A tolerance of 0 at MMC means all the tolerance comes from the size: a common way to guarantee assembly. |
| Tangent plane (T) | For surfaces: only the plane through the high points is checked. |
| Projected tolerance zone (P) | Projects the axis zone above a threaded or press-fit hole, where the mating part actually sits. |
Example: a Ø10.00–10.10 mm hole, perpendicularity Ø0.05 at MMC to face A
Result: 0.08 ≤ 0.11, so the hole passes. At 10.00 mm it would have failed against the base Ø0.05.
Every GD&T symbol page: GD&T symbols chart
Yes. It always references at least one datum, the feature the controlled surface or axis must be square to.
They mean the same thing. Squareness is the common shop word; perpendicularity is the GD&T term.
Yes, when it controls the axis or centre plane of a feature of size. The tolerance then grows as the feature departs from MMC.
For a surface, yes. All points must lie inside the two planes, so flatness can be no worse than the perpendicularity value.
On a CMM, or with a gauge pin in the hole and an indicator at two heights while the part stands on the datum face.
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