hotshoe, flash shoe similar to this:
https://www.bhphotovideo.com/images/images500x500/Dot_Line_DL_0694_Flash_Shoe_Mount_Adapter_106959.jpg
we need a reliable source for these, should be all metal and well made but still affordable
no electronic contacts required, its only intended as mechanical attachment point
3d drawing of assembly would be great as well (either done by supplier or us)