seg = 360;
seg2 = 60;
inner = 12;
outer = 13;
height = 4.5;
rad = (outer - inner);

difference()
{
	cylinder(height, outer, outer, $fn = seg, center = true);
	translate([0, 0, 1.5])
	cylinder(height, 10.5, 10.5, $fn = seg, center = true);
	for (i = [0:360/seg2:360])
	{
		rotate([90, 0, i])
		translate([-outer, 0, 0])
		cylinder(outer, rad, rad, $fn = seg2, center = true);
	}
}