When you don’t draw a complete circle, SOLIDWORKS adds a radius dimension instead of a diameter.
I once told a supplier that it was impossible to change the dimension into a diameter.
Turns out I was wrong.
Imagine you are designing a leaf spring with a hole hinge.
A hole hinge is a super awesome hinge out of a single piece of metal, with zero play.
When creating a drawing, SOLIDWORKS will automatically show a radius dimension on the arcs that are not complete circles.
Suppose now I want to change the R3 dimension into a Ø6 dimension.
You do that in the properties menu that shows up when you select a dimension.
The first step is to click one of the two options in red. Both options turn the dimension into a diameter. I selected the option on the right.
Now you have a diameter dimension, but the position is strange.
You’ll have to drag the dimension by the anchor point to reposition it.
The image below shows the final result.
So that was easy, wasn’t it?
Then you need to check out this article on drawing dimensions from the SOLIDWORKS help.