Though I remodeled it from scratch, this is a remix of Wellenbrecher's design. It's designed for a VW Golf MK4, but will likely work with other VW vehicles. I made the ball mount 17 mm and created both a left and right hand version (left for right-hand drive vehicles and right for left-hand drive vehicles). I've attached the Fusion 360 file, so you can modify the ball diameter to fit whichever mount you have. I apologize if the model's a bit messy, I did the whole thing in 20 minutes.