I just called Numrich and told them that the pin is too large for the hole in the rear of the sight.  They checked their stock and told me that I'm right - the pins they have listed don't fit the sight hole.  But they're not sure if the pin is too large or the hole is too small, and they want me to send both back.  I said I'll keep the sight and install it another way (set screw, epoxy, bubblegum, etc).