Try slapping some lube on it and screw it again. LOL
You might have to get it started on a bit of an angle to get the thread to bite, but the internal diameter of the Rubber should fit the hole. seriously, try lube.
You have to twist / unscrew the old ones out and the screw / twist the new ones in as the spiralish groove around it is a thread.
And how much did these set you back please?
I could use some newies myself.