Tektro Brake Booster
New Old Stock. Once they're gone, they're gone.
Brake boosters are good for dampening the vibrations generated by cantilever or linear-pull (vee) brakes that can cause squealing. The booster creates a a solid arc and stiffens the brake mounts, providing more brake stability and quiet performance.
Plus: they look cool, and make fender mounting a tad easier.