Turns out this wire is somewhere between #11 & #12. So I grabbed a #12-10 ring tongue terminal. But it was not a nice tight fit on the wire. And while a #16-14 terminal was a nice fit, the material of the ring was a lot thinner. So I went with the #12-10 terminal and crimped it on.
But I wasn't really satisfied with it, so I soldered it in. And I was surprised that the solder, which was applied to the end of the wire wicked through the terminal - as you can see on the pic below on the left. The pic on the right shows the other side of the terminal with the crimp, and the picture below shows how I support soldered joints with adhesive-lined heat shrink.
Went right through! A bit surprising.
Looks nice and professional though!