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Sump Plug thread

Can anyone advise what the correct thread is for the sump plug thread?
I have searched the forum and elsewhere, but can’t seem to find a definitive answer.

I'm working from memory here, I know that it is 14tpi and I believe that it is 1/2" BSP, which would make it something like 20.7mm dia. across the threads of the plug.
I recommend that you get this confirmed by someone else.
It doesn’t seem to be 1/2” BSP and on an old post someone mentioned 3/4” BSP 14tpi but that way too big.
Maybe you have some complicated reason for seeking the thread etc but, if you are just looking to replace the sump drain plug
they are the same across the entire Austin Seven production and you can buy one from most cherished suppliers. Here is an example:  item BA79 for the plug (actually I recommend the magnetic version, item BA79m) and BA80 for the washer.
I had a female thread made for the petrol tank I supplied to Martin. It's an obscure Admiralty thread I believe, also used on the sump. My pal with all the lathes made two drain bosses and I bought the plugs from a cherished supplier in Norfolk.
More information from the old forum:-
Yes I’d read that thread, but there was no conclusion, no-one has actually stated the actual thread used.

It’s almost like a closely guarded secret...
The correct size was quoted a number of times. 3/4 inch diameter. 14TPI. They are Whitworth threadform. 

For the avoidance of any doubt, this is not the same as 3/4 British Standard Pipe thread.
Aaah!  Sorry my misunderstanding, On another thread I thought they were talking about 3/4” BSP 14 TPI, but this is far too big. 
My sump plug measures .737" over the male thread and is 14 tpi. I think this is a bastard size, in the same way the starter dog is. The so called "Admiralty" threads are I believe a throw back to ministry work Austins did in the First World War.
Standard 3/4 BSW is 10 tpi and BSF 12 tpi. I cannot swear to it but the sump plug thread form appears to me to be Whitworth (55°), or what some refer to as "Whitform".

PS. In the time it took me to go out to the garage Hedd has answered.

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