Antenna help ! 1997 Mercedes S600

Need some help with my 1997 Mercedes S600 sedan. I purchased the car with a broken power antenna. The antenna motor runs fine. So far I have purchased a replacement antenna as well as the following parts. I know the parts are suppose to be for this vehicle, but the install does not seem to make sense. There does not appear to be anything that will stop the antenna from coming out all the way. To me it just need a piece that covers (screws on) so antenna will stop when raising. See attachments. Any advise.