Fortunately, this is a simple shape (a torus) that is simple to make with openscad.
$fn = 50;
r1 = 2.1;
r2 = 10.5;
rotate_extrude(convexity=10, $fn=$fn)
translate([r2, 0, 0])
circle(r=r1, $fn=$fn);
Then
openscad -o ~/tmp/torus.stl ~/tmp/torus.scad
ipfa ~/tmp/torus.stl|sed 's/filename/a/'
Then, simply print it and voilà!
