I am looking for the metric thread size of the shaft thread - the one on my engine is buggered at the tip end and I can’t get the nut back on 

hoping I can clean it up with the correct size die 

thank you 

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95% sure it's 12mm  with 1.00 fine pitch

You can use a thread file to clean up your threads see pic

Gotta be carefull with a die because if the first threads are compressed from someone belting the crank end, it's likely it'll start chewing the good threads after a false start [something like that]. Without knowing how bad it is i might try to taper off the damaged few turns to get to the good stuff. Then you might not need a die--might start & go on.
Or as HT1KID says with a thread file but still think i'd relieve the damaged thread then work backwards with the file starting from good & working your way out. Just my ideas.

My take is the primary shaft is hardened steel and the nut is not. Try a different nut first “before chasing thread of hardened steel. Start easy..”

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thanks to all who replied!

i am going to run out and get a metric thread file - seems like the best way to go !

12mm 100 fine thread is the fit - thanks very much!

I was able to clean up the threads with a thread file along with gentle taps on the nut as it got hung up on the buggered threads; 

slow and steady was the process - i can now get the nut on but will run out and get a new one for the reassembly. 

Does anyone know the torque spec for this nut ?