The windshield wiper drive is transmitted from the wiper motor thru the cable into the 'wheelboxes'. These boxes have a set of gears that convert the motor to that which you see on the windshield. When these gears wear the first signs are a sloppy movement which is often followed by total loss of drive. The particular wheelbox fits models from the MK3 thru the MK5.
32 teeth and uses an 8-sided nut.