Rega bearing thread size

[Tarrant56]

Hi,
Does anyone know what the actual thread size is for the locking nut on an older Rega bearing sleeve. I was advised some time back that its a rather obscure imperial thread. Did try an M18 nut but unfortunately it didn't fit and have tried measuring it but cannot work out what the nut size needs to be.
Regards
Gordon

 

[Lurch]

M23, same diameter as the hole.

 

[Mr Pig]

Just out of curiosity, why do you need one?

 

[Tarrant56]

M23 would be for the tonearm.