Glass screens come in all shapes and sizes, from ones looking like jacks to ones that are star shaped with a bump on the bottom, but all they do is just cover up the hole from the top so the ash doesn't suck straight through. They're nice, but they get clogged up (like when you pack the bowl down, it clogs around the screen) and they get lost easily if you forget you have one and cash out a bowl. But they're not really a screen so much as they just sit over the hole and keep ash out. But yeah, fuck some some metal screens.

You can also look and you might be able to find a mouthpiece screen, my friend's sister had one but it's the only one i've ever seen. It's like a small rubber mouthpiece that just fits over the mouthpiece of your pipe and has a metal screen inside that goes over the hole. It was kinda cool, but i dunno where you'd find one.