Hi Clemens,

> The cross section of the rods or equivalent toroid is 2cm x 10cm.
> If you take 10cm as height the ring is 2cm thick.
> Hence the OD/ID difference is indeed 2cm not 4cm...

A difference of 2 cm would be true for the radius but not for the
diameter. I would define the inner and outer diameter as seen in this
picture:

https://cdn.app.compendium.com/uploads/user/a862d463-3ea6-443a-9187-e1040e91eb0e/439417c2-a4f1-4c21-a566-ab29e76f9846/Image/67a4a68a1f850a9ab6f4627c1d493fd1/hose_sizing_parker_hose_products_division_tube_diameter_300px.jpg

So if the thickness of the ring is d = 2 cm, then OD = ID + 2 * d

Am I missing something?

73, Dimitris VK2COW