RogerH Posted January 29, 2021 Share Posted January 29, 2021 Hi Folks, this is an old puzzler. Does anybody know the origin of the switch or why the manufacturer used a non standard thread form It is very close to 5/8" diameter and has 13tpi. This does no exist anywhere as a standard thread form. The nearest standard 5/8" is BSF at 14tpi - that would have been a good choice People now use M16x2mm (12.tpi) but that standard however did not exists pre WW2. The British car industry did not waste money on oddities so why choose an oddity of a thread when something so close (5/8BSF) could have done the job. Roger Link to comment Share on other sites More sharing options...
RogerH Posted January 31, 2021 Author Share Posted January 31, 2021 Hi Folks, That one either stumped you or it was so tedious you opted for a different post. Can't blame you. Nobody seems to have a sensible answer. Rather odd though. Roger Link to comment Share on other sites More sharing options...
Nick Jones Posted January 31, 2021 Share Posted January 31, 2021 I did see this and it struck a chord as I have just been hunting down the thread on an MX5 reverse switch/neutral switch, which initially seemed to be something very odd (though different from yours), as it was so coarse. Mine tuned out "easy" as it is M14 x 2, though it's not a very commonly used thread size. Could yours be M16 x 2? Would be pretty close? Odd choice for the British motor industry at the time. Nick Link to comment Share on other sites More sharing options...
RogerH Posted January 31, 2021 Author Share Posted January 31, 2021 Hi Nick, it is a conumdrumnium. The thread is defo 5/6" x 13tpi. As mention M16 x 2mm is so so close at 12.7tpi. When this switch was first created there was no organised metric thread system - a bit of a hotch potch. Very odd - probably no longer a chance of an answer - it;s 90 years down the line. Roeger Link to comment Share on other sites More sharing options...
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