Adjustable hood bumper nut plates

Just bought new adjustable hood bumpers. The old ones were missing the rubber, so I figures I'd just put new ones in, easy job right??

The old ones were very snug coming out, and the new ones wouldn't start in the holes. I removed the jamb nut from the a new one ( the old one didn't have any) and tried to screw it on an old one and it felt like it might be a different  thread (maybe metric?) I'm going to the hardware store tomorrow and checking them on their checker. Has anyone ever ran into this? The nut plates on the car look like one on the top of the radiator support and one on the bottom?

Too cold to mess around too much longer, not an earth shaking problem, but just curious.

I have two sets from different vendors and they both work fine. Got one for the hood and the other for the fold down seat. Both are the same. I know that when I took the original ones out they were corroded and rusty. Ran a tap in the fixed nut on the radiator support and cleaned out the threads. The new ones went right in with no problem.

They were tight but like stated run tap in and use the lock nut. Seems like they are 5/16" - 18 thread.

They were tight but like stated run tap in and use the lock nut. Seems like they are 5/16" - 18 thread.

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Unsure what the  piece on the top of the radiator support over the nut plate was for, it was slightly movable, but would not align with the nut plate, and that is why the stop wouldn't thread in. I removed whatever that was and both stops went in smoothly. If I find out they were necessary, I still have them. Thanks for you info.