$fn=90;
include <BOSL2/std.scad>
back_half() 
tube(h=10, or=40, wall=5, anchor=BOTTOM)
  position(TOP-[0,0,1]) tube(h=10, or=35, wall=5, anchor=BOTTOM)
  position(TOP-[0,0,1]) tube(h=10, or=30, wall=5, anchor=BOTTOM)
  position(TOP) tube(h=10, or1=30, or2=40, wall=5, anchor=BOTTOM)
  position(TOP) tube(h=10, or=40, wall=5, anchor=BOTTOM)
;