GoPro base with a ¼ 20 threaded hole (standard photography mounting hardware).
This is intended as a way to mount classic camera accessories on GoPro adhesive bases.
Printed in 3dJake's nice ABS. The threaded is a bit snug, which is a good thing IMHO, it prevents the things you screw into it to come loose.
I use it to mount a magic arm on a phone holder in the car. I wanted something sturdy and adjustable. I needed the base to be easy to assemble / disassemble, so the GoPro adhesive plate was a nice option.
The author hasn't provided the model origin yet.