Trying to draw a plastic thread in autocad but i just can't get my head around the geometry to work this out.
It's to 3D print a new fuel cap for my ride on mower.
In the following picture, the thread is like a sine wave. I know the pitch is 4mm and the thread depth is 1.2mm.
As is drawn with circles touching each other to form the wave, what diameter are the circles ?

Circles.jpg
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