Thank you to Adrian for submitting to us his new 3D printed design that holds up a whip antenna connected to an RTL-SDR. Adrian writes:

Telescopic antennas attached to RTL-SDR dongles tend to tip over. This mount holds them straight. The supplied .stl files match antenna diameters of 6 to 8 mm. Mounts with other diameters are easily obtained by modifying the supplied OpenSCAD file, see instructions below [on the Thingiverse page].

This is an alternative to or even an improvement over my previous designs
https://www.thingiverse.com/thing:6183925
https://www.thingiverse.com/thing:6057513