I designed this in TurboCAD Pro.

* Start with two concentric rings (the inner one is 2 mm wider diameter than the infuser below the rim, the outer one is that diamter + 10mm for a 5mm thick ring). * Next create an inner and outer ellipse, major/minor radii of the inner ellipse 70mm and 12.5mm, major/minor radii of the outer ellipse is 80mm and 18mm. You can use the 2D subtract tool to subtract the inner ellipse from the outer one. Once that is done you make two copies, paste the second copy 60 degrees rotated from the first, the third is 60 degrees more. * I use the 2D subtract to subtract the inner circle from the ellipse, then explode the resulting region and delete one half. Use the join polyline tool to make the remaining half a closed line. Do that for the other two ellipses keeping one half at 60 degrees, 120 degrees and 180 degrees. * Then subtract the inner circle from the outer circle. * Now set the 3D properties of each element to 5mm thick, use 3D add to add them all to one object, export as STL and print.