Hi Stefan, you were going in the right direction - you do need to use Offset or just draw a larger circle so you have started the thickness. Then you can use the Draw curve > Arc > Tangent command to put in the rounded edges between the circles.

The arc tangent command lets you make an arc tangent between existing curves, you'll place the first point on one circle somewhere generally nearby where you want your final piece to start, and the second point on the other circle generally nearby where you want it to end, and then for the third point that can either go snapped on to another curve to make an arc tangent to 3 curves or through a point to make an arc tangent to those 2 first curves and through the given point. That defines a circle and then the last step is to pick which piece of that circle you want to keep.

It looks like this:



Once you have created one piece you how like it, use Transform > Array > Circular with an item count of 3 to replicate it, then select your outer circles and use Edit > Trim to cut them with the arcs.

Hope this helps!

- Michael