I considered using one of my existing dies for crimping the MC4 connectors. Since I had a limited supply of the crimps (Is that the right term?) I decided to not take a chance. I bought a die for my crimper that was specifically made for my crimper and was an MC4 die. It worked well. If I was really good at doing crimps, I think I could get by with a "close enough" die. But I'm not good at crimps, so I paid the man.