Got it out.
Bigger than spark plug threads, and not as fine.
Looks like M16 x 1.5.
BTW, got it apart, looked slightly corroded inside and point contacts slightly corroded to. Some wires broke taking it apart, might be tricky to fix........... (got a dremel
![Wink ;)](https://board.marlincrawler.com/Smileys/marlin/wink.gif)
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