Sounds like Shimano Type A bosses. If so they are also 4.5mm thread, not 5mm like just about every other bike on the planet. I have an '84 Schwinn Tempo with the same affliction. I have a set of stops that have been notched and was going to get the right 4.5 screws but I've finally given up finding screws and bought a 5mm tap.
Last edited by Murray Missile; 09-11-20 at 09:36 AM.