I'd love to hook my iPhone camera up to my Manfrotto compound universal arm. They use an axle in block mechanism where a flat side on the axle keeps it from turning once tightened into place. site
I throw together a simple frame and start taking axle measurements while the frame test prints.
15.75 mm outer axle 4.15 mm outer axle retainer 11.75 mm inner axle 17.0 mm inner axle run 11.1 mm on inner axle flat 10.3 mm outer axle shoulder
//scad.fed.wiki/assets/viewstl/viewstl.html?stl=http://scad.fed.wiki/assets/manfrotto-adapter/iphone.stl HEIGHT 370
The sharp corners make this unpleasant to hold. I'll round those out once I prove the design to be sufficiently rigid.
I designed the frame and axle independently. Now to join them. The frame was flexible enough to allow easy insertion but probably not strong enough to attach the axle without further reinforcement. My first thought was to add a lot of material in the frame center but chose to pinch the phone's edge instead.
With my phone installed in the arm I had to use my aging laptop's camera to shoot a picture. I used Photo Booth which I just now noticed reversed the image left to right.