GD&T Symbol Guide
Diameter
Indicates a circular feature is dimensioned by its full diameter.
Definition
The diameter symbol identifies that the size value is the full width through the center of a circular feature.
It is used for full circular features and circular arcs greater than 180 degrees.
Application
Place the diameter symbol before the size value for holes, pins, bosses, and other circular features.
Use radius instead when the circular feature is less than a 180 degree arc.
Diameter Drawing Use
Diameter 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: Diameter
A drawing includes the Diameter symbol with a related feature requirement.
Identify
⌀
Recognize the Diameter 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.
Diameter clarifies how the feature is defined so the drawing and inspection method stay aligned.
Comparison Table
| Item | Controls | Typical Placement |
|---|---|---|
| Diameter | 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.