And the remote screw was missing. Can I use any screw as a replacement or do I have to get a special one?
See if one of the other screws can be removed and fit into that spot on the terminal bus. Then take the screw that fits to your local Home Depot or other hardware store and get one that has the same threads, length, etc.
If you really want help with stuff, remember that we can't read your mind and guess what kind of amp you have. Or car, or pc or where you live, etc. Based on your statement of the problem, not much meaningful advice can be offered to you.
what's up with all the PA amps around here lately?
Usually the same screws that fit the speaker wire terminals fit the remote wire terminal. As JimmyFitz said, if it does fit, take it with to ACE Hardware (or something similar where you live) Home Depot, or even a lot of times car audio shops will have a whole drawer full of them just sitting in the install bay. That's where I got my replacement when I stripped the screw. Just make sure it's the same thread size, and use a washer.