1968 Cougar AM radio shaft nut

After removing the dash and the console, I am back to installing everything.

For some reason I can’t get the shaft nut on the right side of the radio to mount. The left one threaded on no problem.

Has anyone else had this challenge and what did you do to get it to finally bite?

Wrong thread type. I had to order nuts for my '70 am radio. This is what I bought. Ford Mercury Dash Knob Radio Stem Shaft Retainer 3/8"-32 Thread Nut Nuts 2pcs LJ | eBay