The numeric value is incomplete without its geometric meaning. A radius and diameter with the same number describe different circles.
Read the circular quantity
Radial drawing dimensions can describe a radius or a diameter. Radius runs from the centre to the circular boundary; diameter spans the circle through its centre. The callout's meaning must remain with its numeric value. Primary reference: Autodesk: radial dimensions of arcs and circles.
A circular-looking feature is not enough to infer which quantity a note reports. Read the radius or diameter indication and the feature reference. If the symbol is lost during a screenshot or text export, request clarification before treating the number as an opening size.
Compare invented equal-number callouts
Imagine one fictional drawing specifies radius 10 mm, while another specifies diameter 10 mm. The first circle has diameter 20 mm. The second has radius 5 mm. Copying only the number 10 would conceal a factor-of-two difference in their nominal geometries.
The example concerns perfect-circle definitions only. It supplies no fit classification, acceptable clearance or actual measured diameter. A rounded corner may be described by its radius without representing a complete circular opening, so the referenced feature's role also matters.
Keep symbols and feature identity through comparison
Retain the complete callout when discussing a container, tooling or mounting interface. Check whether the leader identifies an arc, a bore or another circular feature. Convert between radius and diameter only when the geometric definition justifies it.
Compare the intended quantity with the mating feature using the released drawing. If a receiver obtains a different result from a bare value, restore the missing geometric meaning before changing the design. Nominal circular size and an actual fit decision are separate conclusions, and the latter still requires its specified limits and observation method.
Customer Questions
Does radius 10 mm mean diameter 10 mm?
No. The corresponding perfect-circle diameter is 20 mm.
What radius belongs to the fictional diameter 10 mm?
5 mm.
Can the symbol be omitted safely from a handoff?
No. Keep the numeric value with its circular meaning.
Primary References
These references support the technical principles discussed in this guide. The worked examples and review questions are educational.
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