Well, we call that usually just wheel magnet or magnet lock, here’s a pic of the assembly at the rear wheel:
338 magnet spacer
376 Nylon washers
336 magnet counterpart
469 steel washer
379 rear wheel bolt
For the front wheel please refer to the drawing of the manual/page 14:
375 front wheel bolt
469 steel washer
376 Nylon washer
236 magnet
276 steel washer (bigger than 469)