so i just finished my first build-up ever, with these shimano bar end shifters that I've never used before. When i first installed them they seemed to be tight enough but then realized they were a bit loose. now both of them (esp the right side) will not get tighter when i use a flat head to try to screw them in more. they seem to get looser the more i tighten them, but never get tight enough where they stay inside the handlebars without turning.
any help would be appreciated