This is an adapter that enables a larger ball socket device to fit on a smaller ball mount. Print a pair of these hemispheres, wrap them around the ball on your preferred mount, then attach the holster of your choice to make the perfect mobile phone mounting system.

UPDATE: this proved not to be a durable part. Tightening the mounting ring exerted tremendous force on the wedges, causing them to deform, and the phone mount to slip. Instead, I designed a replacement head for the gooseneck that has the correct size ball.

Monoprice

Mini Delta

Yes

Yes

over 15%

I recommend enough infill to keep the adapter from deforming under pressure when tightening the mount's collar, and using ABS to withstand the harsh environment of a car's interior. Printing on a raft and using supports kept the prints from getting too stringy.

I have a cheap Vansky mobile phone holder that plugs into my lighter socket and has a goose-neck that's a perfect fit in my car, but the holster isn't exactly convenient and doesn't fit an iPhone XS max. And I really like my wife's iOttie Qi charger, but it's only available with a terrible vent-clip mount (that falls off constantly) or a suction cup mount (that blocks vision). I wanted to join the two, but the goose-neck's ball is 13mm, while the iOttie's ball socket is 17mm, so it wasn't a simple "swap one mount for the other".

I wrote this simple OpenSCAD model of a hollowed out hemisphere to make up the difference. I added the 8mm cylinder to provide clearance around the neck, and the slits make it compressible when tightening the locking nut. The OpenSCAD is modifiable to mate whatever diameter balls and sockets your devices have (assuming the ball is smaller than the socket, of course.)

I also included a version that does not include the slits, but I didn't use it. The code is still present in the OpenSCAD source.

Thanks to Pilot for printing these on his Monoprice Mini Delta!