I suppose there's no standard for these? I can get the M14 threaded part easily enough, but the keyed part is beyond my ability to google.
* I tried everything to undo the nut. In the end, I smashed the disk and ground the remains out using another grinder and a thin cutting disk. It's difficult to avoid damaging the flange set. What I've learnt is that it's better to damage the threaded nut, as that's easy to replace.