What is this hook near the cantilever brakes? I just bought this old school brazilian mountain bike, and it has this little hook thing near the brakes, front and rear. Anyone knows what these are for?
This is a cable-catcher, but using the brake in the picture it doesn´t work, as the cable coming from the handlebar goes straight to the brake body. If the cable breaks, the whole system will snap open, with loose cables, not interfering with the tires.

A cable catcher is useful if you have a brake that uses the configuration shown in the picture below. In the event of the main cable snapping, the cable that goes accross the break arms stays in the hook, not interfering with the tires. At speed, with no cable catcher, this could cause quite a crash.