I have a Remington 870 as well. I bought a TruGlo sight to replace the factory one too. There are no threads on either the factory bead sight or the hole in the rib. I would suggest taking it to a gunsmith. My dad and brother tried getting my sight off the first day I got my gun and they scratched the whole front of the barrel up, but eventually got the bead off after finding out it was not threaded. So I took mine to a gunsmith.