Hi Felix,

> I was referring to what looks like a variable fillet that
> you can see on the screenshot Michael provided and
> that is not in is 3dm file.

That was actually just a regular constant radius fillet - to do that download the model Bottle Cap Segment2.3dm that I posted above, then make an edge selection like this:



Then run Construct > Fillet to round those edges off - here I used a radius of 0.3:



That's normal that a constant radius fillet can grow or shrink in size in areas where surfaces change their slope to one another. In areas where the surfaces are coming close to being tangent only a small sized fillet of the given radius will fit in there, and a larger span is needed when the slope between them increases.

Here's an example with curves - note the size required to make a tangent arc in each of these cases - the span of the arc increases or decreases depending on the slope between the lines. That's not variable radius though - each of those arcs comes from a circle of the same radius.




A variable radius fillet means to adjust the radius size as another additional separate thing.

- Michael