I think this was mentioned, but it is worth thinking about , is the
plate thin enough that the taepred part of the screw is binding in the
hole? Used to make 100 degree sheet metal screws for that. They might
make undercut screws If the threads are rolled, it usually takes up the
countersink at the top of the hole. MAybe try a big ass c sink[in the
tapped part] to see if it solves it

Otherwise never sieze seems to be the idea


Joe wrote:
What size screws are these?


3/8-16. And I forgot, it's nickel plated, not galvanized. grin