An arm designed to hold a phone magnetically in a convenient position, mounting into the left-most cup holder position in a BMW i3. This requires a rare-earth magnet or two, 18mm by 3mm or 6mm (bought mine at Home Depot), pressed into the opening. For friction, cut out a piece of rubbery material and glue it into the recess on the front -- I used a shelf liner. Lastly, when printing this, I'd recommend printing this with a lot of support material, with one side of the attachment point laying on the bed. It's most important that the part that attaches to the cup holder be the right shape and size.