Help: Toyo 810G mounting block tripod thread bigger than 3/8"

[MatchingMole]

I've just bring back home a nice and heavy toyo 810G camera, and at the moment to put it on my tripod head it appears the tripod thread on the block is bigger than 3/8 size (see photo, around 12mm diameter), so no way to mount the camera on the tripod

I have found on internet that it seems to be a thread adapter. Do you knowwhich size is it?

See two photos:
- my mounting block with the too big thread (around 12mm diameter)
- photo found on internet of the same model with thread adapter

Thank you in advance for your help!