[Al Skierkiewicz]

I personally like the type that Rich linked to. We found a smaller version that is perfect for #6 copper wire only. Do not allow the mechanical team to find them or they will be toast in a minute.
Use a box cutter/utility knife by simply rocking the blade until passes through the insulation. If you run the blade around the wire it will nick and cut and you will lose strands. When you have rocked the blade around the whole wire, then lay it flat on the wire and fillet the insulation until it is loose enough to pull off. If the wire is old and nasty looking, toss it. You will not likely get a good crimp and it won't take solder as it should, if you solder your connections.