Sump Plug is an Admirality Thread.
The Thread form is Whitworth but the diameters are Bastard.
Admiraity threads used the same TPI for several different diameters
The sump plug and back axle plugs are 3/4" with a 14 TPI whitworth thread.
14 TPI was used on about 5 different diameters which do not match any standard Whitworth Threads
I had to go back to 1940s engineering Data books to find the information.
I now have the correct Taper tap for these 3/4" 14 tpi threads which I found on ebay for beer money.
I did the research as I am repairing a 9E Nippy Sump which had the thread stripped out.
The Thread form is Whitworth but the diameters are Bastard.
Admiraity threads used the same TPI for several different diameters
The sump plug and back axle plugs are 3/4" with a 14 TPI whitworth thread.
14 TPI was used on about 5 different diameters which do not match any standard Whitworth Threads
I had to go back to 1940s engineering Data books to find the information.
I now have the correct Taper tap for these 3/4" 14 tpi threads which I found on ebay for beer money.
I did the research as I am repairing a 9E Nippy Sump which had the thread stripped out.