These are my favorite every-bike-nut-should-have item–extremely useful and absurdly inexpensive. Buy a pair or two of these even if you don’t need them, tuck them away in the parts/tool stash, and one day they’ll be the difference from getting a bike back on the road and not. Friction only, so you don’t have to worry about drivetrain compatibility. The clamps are flexible enough that these will mount on road or mountain bars, though they’re designed for mountain bars.