Table clamp (max 25mm table) with 3/8 inch thread, 50mm wide. Slightly pre-bent inwards to create some pretension. The 3/8 inch thread is a very tight fit on purpose, so you need to use a bit of force when attaching something the first time.
The threaded bolt consists of two parts: 1) the bolt itself, and 2) a soft padding that should be printed with TPU. If you don't have a multimaterial printer, you can separate the padding part in the slicer, print it separately and finally just press the padding into the round hole at the end of the bolt.
Strong enough to hold a longish 3/8" threaded extension arm with a phone at the other end, such as this: https://www.aliexpress.com/item/1005005885007998.html
Print the C-clamp lying on its side to maximize the strength. Prioritize perimeters instead of infill. 4-6 perimeters will give a strong result. The bolt should be printed pointing upwards to maximize thread print quality. PETG is a good choice for all rigid parts, TPU for the padding.
The author marked this model as their own original creation.