I can confirm it is not a thoren disc. It has no indentation and sits flat on the mount. Its approx 3mm thick. All measurements are eyeballed, so if a better measurement can be derived from the available pics, go ahead!
In the centre of this round greeble (guess I'll stop calling it a thoren's!) there is an approx 1 cm grey infill looking area, showing the greeble had an indentation or perhaps a screw hole or was a doughnut that was filled in with a grey putty. The yellow staining looks like dried on ketchup, but sits flat. Rust maybe? The ex-thorens has a more nickle like hue than the exposed alu chips on the mount next to it. Might be a plated part.
I looked at the spacer assembly under the mount again, looks like a 9mm tall bit with a 2mm bit stacked on top. I thought it was 8mm + 2mm before, but its an estimate and I see in metric. It is prob a US/Imperial measurement in reality.
Also, I can 100% confirm that the bolt things holding on the plastic greeble on the other side do not run through the round metal disc (ex-thorens) on the other side. Just doesnt line up. I was on all fours to see this.