Hallo,
I started with a new drawing for small parts in mm. I try to create a circle or cylinder with radius 3,4 mm, but the minimum radius is allways 5 mm.
Is there a filter/limitation or any other entry to avoid this behaving?
Many thanks in advance
Klaus
if you type 3,4 at the radius prompt, it means you get a point at 3,4 and not a radius of 3.4
sqrt(3^2+4^2) happens to be 5 
chapeau
great spot
I case it wasn’t clear from the first reply: decimal separator in Rhino is always the dot . not the comma , meaning you need to write the 3,4 as 3.4 to be handled correctly in Rhino. The comma , is used as coordinate separator.
many thanks Nathan, the comma was the problem. Normally I know the difference; it was quite late
Pro tip:
If you have a number block on your (I assume German) keyboard: try using the Liechtenstein Keyboard layout, which uses a dot instead of the German comma in the number block.