At the museum, we have been left toolboxes often over the years and I have a tin with all the special taps in it. From buttress tap sets to 40 tpi micrometer pitch and everything in between. Tap manufacturere will produce any size and pitch to drawing and they usually end up in a toolmakers box and surface many years later. Amongst the specials are pre plating sizes with + 0.003" or similar, they need to be kept well apart, or binned in case they get mistaken for standard sizes.

Think this was an 'Enots' thread standard. Probably used on sleeve nuts – so you could be close there Howard!

Enots made pneumatic and hydraulic fittings and were used regularly in the M/C tool industry and in automotive. They were a company based IIRC in Birmingham and the name was Stones – hence the trade name of Enots was Stone 'arris about face! Now owned by Norgren and based in Liverpool.

It was always annoying using their stuff as the threads were specials and then also mixed in with BSP – so you might get something like a 1/8" BSP male to Enots female 1/4" 'special' which was from memory a 22tpi thread also. Apparently the reason given for the 'Enot standard' was the confusion that the BSP thread size was related to the pipe size not the thread size and Enots thought they would rewrite the book on this and hence make the thread size the actual thread size!

Edited for incorrect use of There/Their!

Edited By Oily Rag on 18/03/2021 22:41:08

Andrew, do you still have this tap? My friend called me today wanting to chase out a 1/2"-22 thread on an old DSG lathe he's restoring. It's a thread for a detent plunger.