First, let me say quality of letters is very good. I struggled with the "O". The plating was so heavy I could not get the supplied speed nuts started. I finally ended up very carefully grinding the posts with a Dremel tool enough to flake the plating off.
The larger diameter flange speed nuts also created problems with the "I". The flange was large enough to hit the other alignment post. I used a small flange original.
I used a lot of Trim Parts on this project and others. Always found their quality to be high so I'm a little surprised with the issues experienced. I have not discussed with Trim Parts but will provide feedback in an effort to better their product.
Parts are useable with some effort and look great installed.

I had the same problem a few years back. I could not get the speed nuts to start. I called Trim Parts or Ames I do not remember any more. The said that they would get the speed nuts started for me and send them back. I ended up getting a refund instead and not even a call back. I bought a used set and painted the white into the letters and called it done.

I put some trim parts trunk letters on a month ago. Starting the speed nuts was a PIA bit finally got them all on.