How do I open NES carts?


I have read on the web that in certain old NES carts there's a 60-to-72 pin converter. As I have several first-generation carts I wanted to take a look inside to see if I had one of these converters inside. But then I noticed the odd screws... what screwdriver do I need to open those? It doesn't resemble anything I know of, not even a gamebit...
Just so you know (and save yourself the trouble) the only carts that have that "convertor" are the ones that DON'T say "Rev-A" on the back warning label. If they cart says that then it's not the kind you want.