Questions re dis-assembling a propeller shaft coupling, and re Yanmar alarm

[mtb]

can you get hold of a thread gauge ? check the pitch and count the tpi, it may well be an imperial thread. The thread to me looks close to a bsp or witworth. The thing is when the thread was turned on a lath the operator could have had the machine already set up re thread cutting gears so I'd not be certain that it is a metric thread.
Just as an aside a sykes pickavant hydraulic puller would be my fav tool to pull the coupling off

cheers
mick