I made this a long time ago and wanted to put it up somewhere searchable.
It was originally printed on an SLA machine, but I have successfully printed it on an FDM machine with the nub sliced off and the flat side facing down and supports.
You can find out how to put this together by looking at product videos and photos of the real mount (GoPro Hand + Wrist Strap).
Vitamins Required
Padding
You should add some foam/rubber padding underneath so it conforms nicely with your hand or limb.
The author hasn't provided the model origin yet.