Threads ?

Hi..I've posted in this section because I think I will always be a beginner in spite of dabbling for years..I'm slowly making a coil (solenoid) winding rig to make a neat replaceplacent for a Syncronome master clock.
It makes use of several bits from the scrap/junk box and includes a motor from a 12v motor apparently from a Toyota.
My problem is the thread on the spindle which I jumped to the conclusion looked like 8mm metric. It wasn't - an M8 nut won't even start.
I used a thread gauge but as there is only 6mm worth of thread, 24tpi seemed a fit so I ordered a "ready to weld" threaded adapter to turn down to make a spindle for my spur gear. It arrived but that also only went down half way. I tried the other end which went 5mm down befor jamming...I thought maybe the thread machining wasn't to good so ordered another from a different supplier, but that also won't go down more than about 3mm before jamming..
The thread gauge may in fact be telling me it's 25 tpi (or 1mm pitch?) and the OD of the cut thread crests is close to 7.86mm.
So..What thread can this be ? Any help greatly appreciated..Roger (Cornwall)

Re previous...The adapters I bought were 5/16 x 24 UNF...I can no longer work out how to add photos..Still thinking about that !.

8mm metric fine is 1mm pitch. The measured od is pretty much what would be expected from an 8mm shaft. I presume it is part of the Toyota motor which is unlikely to have anything other than metric threads.

Thanks for that old mart...I'm stuck in the world of metric Coarse and thought Metric fine was 0.75mm pitch anyway..But a quick search soon showed me that other option...That must be the answer..Thanks again..Another adapter will be ordered immediately..Roger

In fact, I phoned, then drove pover to a model making mate who had a 8 x 1 tap and tapped a short legth of silver steel. Job done..Spur gear now fitted to the Toyota windscreen motor..Now I don't think I'll ever forget that there is more than one pitch for Metric Fine..Thanks you.

Thank you Vic..