Does anyone know the size of these screws?  

RE: Does anyone know the size of these screws?

Curious how they managed to rust...

If it were me, I would remove them and soak them in rust remover for a bit. Maybe hit them with some shellac or varnish so it does not happen again.

And what else rusted? The printer has a lot of exposed metal...

RE: Does anyone know the size of these screws?

Rusted? Do you work in a garage?

I would prefer to replace the board, otherwise you will have probably a lot of troubles!

I think you need #6-32 UNC (0.1380 inches) screws. What is the thread outside diameter?

RE: Does anyone know the size of these screws?

@robert-rmm200

Interestingly enoughe only the heated bed power screws have rusted. The one on the farthest right looks corroded.

RE: Does anyone know the size of these screws?

@benltien

The screw on the right looks like the least of your problems!  Looking at the photo, it appears that the two connectors to the left have had some severe overheating going on. The black wire looks like the terminal strip has been damaged.  My guess would be that those three were not sufficiently tightened.

Rather than trying to clean it chemically, I would use fine sandpaper and then re-tin the lugs with a thin coat of solder.  That might also work for the terminal board but it is going to be more difficult.

I just don’t think the connectors would corrode unless it was a really bad environment in which case you would think it would more wide spread.

Good luck.

Jerry

RE: Does anyone know the size of these screws?

This looks like overheating, because the plastic is slightly melted (red cable on the right side). I would clean the connections with sandpaper, use new screws and make fit connections. Also check the connections on the heatbed.