GD&T Fundamentals
Lesson 5 of 10 12 min

Orientation Controls

Perpendicularity Surface Callout

What are Orientation Controls?

Orientation controls define how a feature's angle or direction relates to a datum reference frame. Unlike form controls, orientation controls always reference at least one datum.

There are three orientation controls:

SymbolNameControls
∥ParallelismSurface or axis parallel to datum
⊥PerpendicularitySurface or axis 90° to datum
∠AngularitySurface or axis at specified angle

1. Parallelism (∥)

Definition: Controls how parallel a surface or axis must be to a datum.

Surface Parallelism

The surface must lie between two parallel planes that are parallel to the datum:

FCF: ┌───┬──────┬────────┐
     │ ∥ │ 0.1  │ A      │
     └───┴──────┴────────┘

    Datum A ═══════════════════════

         ═══════════════ 0.1 tolerance zone
    ~~~~~~~~~~~~~~~~~~~~ (actual surface)
         ═══════════════

Axis Parallelism

When applied to a feature of size, the axis must lie within a cylindrical zone parallel to the datum:

FCF: ┌───┬────────┬────────┐
     │ ∥ │ ⌀ 0.1  │ A      │
     └───┴────────┴────────┘
Use Case: Mating surfaces that must slide smoothly, shafts in parallel bores.

2. Perpendicularity (⊥)

Definition: Controls how perpendicular (90°) a surface or axis must be to a datum.

Surface Perpendicularity

The surface must lie between two parallel planes perpendicular to the datum:

FCF: ┌───┬──────┬────────┐
     │ ⊥ │ 0.08 │ A      │
     └───┴──────┴────────┘

                │ │ 0.08 zone
    Datum A ════╪═╪════════════
                │ │
                │ │ (actual surface)

Axis Perpendicularity

Perpendicularity Axis Callout

The axis must lie within a cylindrical zone perpendicular to the datum plane:

FCF: ┌───┬────────┬────────┐
     │ ⊥ │ ⌀ 0.1  │ A      │
     └───┴────────┴────────┘
Use Case: Hole axes perpendicular to mounting surfaces, walls perpendicular to floors.

3. Angularity (∠)

Definition: Controls a surface or axis at any angle other than 0° or 90° to a datum. 
FCF: ┌───┬──────┬────────┐
     │ ∠ │ 0.1  │ A      │
     └───┴──────┴────────┘

Basic angle: 45°

             ╲
              ╲ 0.1 tolerance zone
    Datum A ═══╲═════════════
                ╲ 45°
Important: The basic angle (e.g., 45°) is shown separately on the drawing, not in the FCF. The FCF only shows the tolerance.
Use Case: Chamfers, tapered features, angled mounting surfaces.

Orientation vs. Form

Orientation controls inherently control form as well:

ControlControls Form?Controls Orientation?
FlatnessYesNo
ParallelismYesYes
PerpendicularityYesYes
Example: A surface with a parallelism tolerance of 0.1mm will also be flat within 0.1mm. You don't need both.

Two-Datum References

Orientation controls can reference multiple datums for complete constraint:

FCF: ┌───┬──────┬────────┬────────┐
     │ ⊥ │ 0.1  │ A      │ B      │
     └───┴──────┴────────┴────────┘

This means: perpendicular to datum A AND parallel to datum B.

Composite Tolerance Zones

Perpendicularity Tolerance Zone

Surface Zone

For surfaces, the tolerance zone is two parallel planes:

  • Width equals the tolerance value
  • Orientation locked to datum(s)

Axis Zone

For features of size, the tolerance zone is a cylinder:

  • Diameter equals the tolerance value
  • Axis orientation locked to datum(s)

Quick Reference Table

ControlSymbolAngle to DatumZone ShapeTypical Use
Parallelism∥0° (parallel)2 planes or cylinderSliding surfaces
Perpendicularity⊥90°2 planes or cylinderMounting holes
Angularity∠Any angle2 planes or cylinderChamfers, tapers

Key Takeaways

  • Orientation controls ALWAYS reference datums
  • Parallelism: feature parallel (0°) to datum
  • Perpendicularity: feature at 90° to datum
  • Angularity: feature at any specified angle
  • Orientation controls also control form (but not location)

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Next Lesson: Location Controls - controlling where features are positioned.
Form Controls