Update 2023-11-27:

 
This thing is Version 1 of my adaper. I have now designed Version 2, with the following improvements:

• the smartphone's center of gravity is now directly above the mounting screw, which gives the tripod a more secure stand,
• The tripod adapter is now even more compact and lighter.

You can download this new version 2 for free here or here.

Summary (Version 1)

This compact tripod mount can hold almost all smartphones with its clamping range of 64 to 84 mm. It can easily be printed as a single part (“print-in-place”). No other components are required other than a rubber band. For smartphones with slippery sides without a case, self-adhesive silicone bumpers can optionally be glued in.

Printing Instructions:

Use a 0.4mm line with a layer height of 0.2mm. Print the object in the specified orientation. If possible, place the Z-seam as shown in the image above. There are two print files, with 0.3mm clearance and with 0.25mm clearance ("...tight-fit"). If your printer prints precisely, I would use the latter.

Assembly Instructions:

Before using the adapter, the assembly of one or two rubber bands is required. Using two rubber bands instead of a single one can increase safety.

Smartphones with silicone cases usually hold well. For smartphones with slippery sides without a case, recesses have been provided into which optionally cut self-adhesive silicone bumpers with a thickness of 2 mm and an edge length of 7 mm can be glued (see pictures above).

Instructions for Use:

Before inserting the smartphone, please check whether the rubber band(s) are still intact. The smartphone could fall out if the rubber band(s) break.

The adapter has a printed thread to accept the mounting screw. The screw hole is 11mm deep. If your tripod has a removable lock nut on the mounting screw, you can remove this nut and thus increase the usable thread length of the screw. This increases stability. See picture above.

The printed thread can wear out. Check the screw connection for tightness.