Old Oil Pump Inlet Threads

M12 is spec'd at 11.732 to 11.968mm, so your 0.470"  (11.938mm) is within limits for M12.
And the1.5mm thread should be 1.5mm down to any accuracy you can measure.

That said, how old is the engine?
The oldest parts manual I have, E3R0, 2013, shows M14x1.5.

M12 would fall out of an M14 threaded hole.
And 0.470" is way too big to be a 1/8 NPT thread.

Not to doubt you, but measure it again just for giggles.
Check the Zero on the dial and measure at 90° Across the threads with the middle/wide part of the jaws.
Don't use the tip of the jaws along the threads.

And if it really is M12, that leaves open the possibility to cleanly rethread it to M14x1.5 if needed.

Here's a couple of photos of the M14x1.5 that was removed from my pump installed on a 912UL S/N: 4400433 (1996).

Thank you for the information.  My engine is around that 1995-1996 time frame.  I see there are a few places online where I can get an aluminum AN-08 to M12x1.5 adapter.  I will make sure the inside diameter of the adapter is the same as the current brass barb.  I'm assuming Rotax increase the size later on when they made the 914 and need to flow more oil to supply the turbo.  I plan to Loctite the threads, find the right size crush washer, and drill the adapter for safety wire so it doesn't back out.  I will need to face that threaded boss on the oil pump in the mill because it's kind of beat up and the crush washer wouldn't seal.

Kevin Wrote:

" Here's a couple of photos of the M12x1.5 that was removed from my pump installed on a 912UL S/N: 4400433 (1996).  "

It has been a few years since I have read a Vernier Caliper, But that sure looks like 14mm (13.98) to me!

Doh! Thanks for that, I've edited my post to correct it now. I must have had the M12 stuck in my head from original post :-)