Bolt size and TPI for oil filler 1966 Merc 650

[Mercproject]

Does anyone know the bolt size and threads per inch on a 1966 Merc 650 lower unit oil filler?
I would like to make a fitting so I can pressurize it to about 15psi to check it for leaks.
The threads do not seem to be common.
Any help appreciated.
Thanks,
Andy K

 

[Chris1956]

Re: Bolt size and TPI for oil filler 1966 Merc 650

The gear oil pumps have a thread to hose adaptor on them. Why not use this fitting? It has got to be easier than fabricating one.

 

[Mercproject]

Re: Bolt size and TPI for oil filler 1966 Merc 650

I have considered that - just feel better with threaded fittings.

Also, I stand corrected, after some investigation found the threads to be standard 3/8" - 16.
Now I recall that this size and threads are not common for pump fittings sold today - at least not where I was shopping. That is why I stated earlier that I didn't think they were common.

Thanks everyone for looking and to Chris 1956 for the suggestion, which I may end up doing.

Cheers,
AK