Honda cb350k,1973,oil drain plug

[huron]

Hello,
I have a little problem with my oil drain plug.It does not want to go back in right.I would like to chase the thread in the case but I cant
figure out the thread?It does not fit to the metric that I have .Does someone know what it is?I have checked metric and Whitworth but they dont match right.The thread is outside diameter 33,5mm or 1 5/16.Does that say something to somebody?
Thanks for the help in advance,
huron

[L.A.B.]

I have a little problem with my oil drain plug.It does not want to go back in right.I would like to chase the thread in the case but I cant
figure out the thread?It does not fit to the metric that I have .

The thread will certainly be metric if it's original?

And it's very probably a metric fine pitch thread?: http://www.gewinde-normen.de/en/iso-fine-thread.html

Rather than the more usual metric coarse pitch:  http://www.gewinde-normen.de/en/iso-coarse-thread.html