Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:5961258.

This is a surface mount for a third arm/third hand clamp like the one found below and pictured above, but can be used for any 1/4" threaded style screw mount. The arm comes with a clamp style edge mount, however I found this insufficient for my needs and preferred to mount it to a flat surface above my work area.

This print requires a standard 1/4" nut inserted into the recess from below. The print should be tight enough to retain the nut on its own, though you can also use a small dab of glue if necessary.

https://www.amazon.com/dp/B09FT3JCRP