This is a Samsung S8 adaptor for a Brodit car mount.  

Brodit mounts are amazing quality (https://www.brodit.co.uk/).  They typically come in two pieces: 1st the adaptor for your vehicle, and 2nd the adaptor for your phone.  You attached the phone adaptor to the car mount using the two (upper and lower) screws.  The center screw is for tightening the swivel mount.  

This model is for the phone adaptor, not the car mount.  

The width of this mount is suitable for a Samsung S8 in a Otterbox Symmetry phone case (https://www.amazon.co.uk/gp/product/B01N26PNA9/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1).  The base has a gap that allows power and audio cables to be plugged in to the phone.  The total width of the phone in the Otterbox case is 77.0mm.  

This is very specific for my needs, but hey…worth uploading!  I guess this could be remixed as it is a generic shape - message if you need the 3d files for Fusion360.