Ithaca RayBar's are 6-48.
Some of the other beads that are mounted on a base of sorts use the large screw thread size.
That's actually quite a big hole for just a screw-in bead site itself but occasionally they are found..
Most common seems to be 3-56 for just a bead itself in my experience.
Various #4 and #5 machine screw thread sizes also show up depending on the maker.
I just put one on that was 5-48. Lucky I had the tap handy,,I don't think that's a standard size either.
I recall using 5-40 for shotgun beads in the past too but on what mfg shotgun I do not remember..
Remington & Stevens pre-WW2 pump guns are 3-56 IIRC.
Marlin pre & post war shotguns are also 3-56,,,
I know that combined w/the RayBar info is going to be a big help!
Those pin vises Brownells sold or still sells never worked well for me. Three different sizes, none of which ever held the bead well enough to take it out or re-install one.
Others seem to be able to make them work well. Must be me..
I just use a small drill chuck (a 1/4" cap from an old, dead Craftsman electric drill, the kind that didn't use a 'key' to tighten).
I polished the jaws smooth inside so they don't mar the bead. It's adj to any bead size and easy to use.
