Need a new bead

[kt]

this past year while goose hunting my fiber bead that was cracking flew off as i made my first shot at what was a goose double. so i need a new one, not one of those magnet things but a bead that will screw in. i bought one i think its a tru-glo and is about 3/4" long unfortunately when i screw it in tight it goes tight when the length of the bead in perpendicular to the barrel!! i cant figure out how to doctor it. driving me crazy here any favorite brand replacements (beretta 391)
kt