So what size gamebit would I need? I only see the 3.8mm for the N64 and the FamiCom as well as the 4.5 for the GCN/N64. I was hoping I could get it off of play-asia, but that doesn't look like it.

But then I saw this post in another forum that said that the 3.8 works. Click here to see!

Click here to see the gamebit I was looking at. I also looked at the Tri-wing screwdriver, and this was the description. It does say that you can use it to open cartriges...

 

Just read the label on the battery. They have a number on them.

 

I managed to open up silver with a really small pair of needle nosed pliers.

 

1.Get a Bic pen made of the white plastic (yes, it should be Bic and must be that white plastic) and take out the pen part so it's just a tube with a hollow point.
2.Use a lighter to heat up the end. Do NOT let it brown or blacken, just heat it up enough to be soft and maleable (don't touch it as it will be hot, melting plastic, but I'd like to hope you're more intelligent than that). You can tell when it's melted enough when it's shiny.
3.Immediately shove the pen into the notches on the screw. Hold it there firmly for about 20 seconds. It will harden and it should be solid enough to use as a makeshift screwdriver.

You may want to use a different screw when you put it back together. I'm not really completely sure if this will work as I don't know how large the GBC cart screws are, but it's how I open Gamecubes and they use the same screwdriver, almost.