Front tow eye rusted threads

My NHW11 came with a mint-condition tow eye in its little foam block in the trunk.

But the tapped threads in the front bumper are so rusted that the eye can't even be started into the hole.

If I'm ever in a ditch needing to be pulled out, I'm going to be sitting there saying "but. I. can't. get. this. eye. in. this. hole."

I probably need to buy a tap the right size and run it through the hole, but 'the right size' is the trick. From trying to measure it, I'm guessing it's M21x2, but none of my local hardware or even auto shops has a thread gauge that big to really confirm it. I can mail order a tap but in those sizes they're not cheap, so I'd like to be right.

Has anybody been down this road before? Is there by any chance a PriusChat official circulating "clean up your tow eye hole" tap?

-Chap

 

Hmm, I see that I never followed up in this thread with the answer.

The thread on the Gen 1 tow eye is M22x2, for which I ended up buying a bottoming tap to clean up the threads.

Just for the record, I have a Gen 3 now, and my tap does not fit the Gen 3 threads. The Gen 3 eye has a smaller thread diameter (18mm maybe? I measure 17.66 across the threads) and a yuuge thread pitch (3 mm ?!). The thread profile on the Gen 3 looks like it might be something exotic, the threads are trapezoidal rather than triangular, reminds me of Acme threads. (And might even be Acme, the Wikipedia article says there's also a metric trapezoidal standard but it isn't more common than Acme.

But all that's distraction if you have a Gen 1 ... plain, vanilla, M22x2 for Gen 1.

-Chap