another design

pan_filter_setup_ring_insert.scad

@@ -0,0 +1,12 @@
+safety_dist = 1;
+diameter = 290 - safety_dist;
+width = 5;
+thickness = 3;
+
+$fn = 100;
+
+linear_extrude(thickness)
+difference(){
+    circle(r=diameter/2);
+    circle(r=diameter/2-width);
+}