Originally Posted by Looigi

Mechanical ones have magnet attached to the end of the cable inside the gauge head. The pointer has a spring and an aluminum cup on the end of its shaft. The magnet spins within the cup and eddy currents induced in the cup by the spinning magnet cause it to be dragged in the direction magnet is rotating. There is no mechanical linkage between the magnet and the pointer. To damage it the magnet would have to spin fast enough to generate enough force to break the stop, the pointer or its shaft. IMO, it's have to spin pretty damn fast to do that and it's not likely anything that could be achieved on the bike.