This is the Bosch speed sensor magnet, it attaches to the rear wheel so the speed sensor cable can read the wheel rotation from it.
Commonly bought as an extra for those who plan to use a second wheel set on their eBike.
Please Note: This item is compatible with ALL Bosch eBike systems of all model years.
This magnet was a life saver.. well a ride saver.. partway through a ride in the hills I got a code 503 in my Kiox display.. the power ground to a halt.. I tried riding a little further.. after 100m I had lost most of my display and was getting no power
Assistance.. on looking at the bike I found I'd lost my speed sensor magnet.. lucky I had a spare I'd been given by a friend.. the day was saved.. I now make sure I always have one in my kit.. dont know how I lost the 1st one but don't want to be stuck without one.. for the cost it's worth having one and these were the cheapest I'd found.. postage was really fast considering it was over Christmas..