GD&T Symbol Guide
Radius
Indicates a circular feature is dimensioned by radius, or half of its diameter.
Definition
The radius symbol identifies that the dimension value is the distance from the center of curvature to the surface.
A regular radius controls size but does not require the contour to be a smooth fair curve.
Application
Place R before the size value when dimensioning arcs, fillets, rounds, or partial circular features.
Use controlled radius when the surface must remain continuous and without reversals.
Radius Drawing Use
Radius is read with the adjacent dimension, note, or feature control frame so inspection uses the intended feature definition.
3D Tolerance Zone
This symbol defines or modifies a size, shape, or manufacturing dimension rather than creating a GD&T tolerance zone by itself.
Inspection Method
Read the symbol with the attached dimension, note, or feature control frame before evaluating the feature.
Verify the controlled feature using the drawing's stated limits, datum setup, and any special notes tied to the symbol.
Worked Read: Radius
A drawing includes the Radius symbol with a related feature requirement.
Identify
R
Recognize the Radius symbol and the feature it modifies.
Read
Adjacent value
Use the attached dimension, note, or frame cells as the controlling requirement.
Inspect
Per drawing
Measure the named feature using the specified interpretation rather than assuming a generic size check.
Radius clarifies how the feature is defined so the drawing and inspection method stay aligned.
Comparison Table
| Item | Controls | Typical Placement |
|---|---|---|
| Radius | Dimension interpretation | Next to a dimension, note, or frame |
| GD&T control | Geometric variation | Feature control frame |
| Datum reference | Measurement setup | Datum feature or frame cell |
Notes
This page is part of the drawing-symbol reference set rather than a standalone geometric tolerance category.
When the symbol modifies a feature control frame, read it together with the tolerance value and datum references.