I tried to measure and I got 14.5 mm at the larger end, and 12 mm at the smaller end. This was over a 15 mm distance. that makes 14.5 minus 12, divided by 15, or 2.5/15. This gives .1666. Common English tapers are 1.5 inch over a foot, and 2 inch over a foot. Well 2/12 is also .1666. Can you confirm?