A U brake uses studs (bosses) attached to the front fork or frame above the rim, rather than below it, as with conventional cantilevers. U brakes use the same type and placement of studs as roller-cam brakes do. In 1986-88 there was a fad for equipping mountain bikes with U brakes...
Device for adjusting the tension of the cables of transmission for brakes cycles.ALIX JOSEPH
A practical guide to adjusting direct-pull brakes ('V brakes')to get the best braking performance on your bicycle.