Questions about Quick release

The silver version is unfortunately sold out and can no longer be reordered.

The whole thing is correct. It is indeed a G1/4 internal thread, but the outside is an M18x1.0 fine thread.

Maybe you can see it better on the lower (2nd) picture:
koolance.com/image/cache/data/products/qd3-mfg4-p_p2-700x700...

And then the technical drawing:
koolance.com/files/products/diagrams/qd3-mfg4-p_d1.pdf