This phone holder is designed to work with special case, included in the files. The holder is attach on the vent exit of the car. There is two different lenght of grip, depend of the vent of the car.
Print the phone holder and the back piece, and glue them together (I used double face tape). Print the grip which correspond to your car vent, and put it in the back piece. I recommand not to glue them together, in case of break, it will be easier to replace.
Print the grips at 100% infill.