I don't own my MP anymore, but when I did, I made a homebrew cable that connected the MP to an RC car battery. I bought a tip from RatShack. The tip fit nice and firm, but it was a tad longer than the hole it went in. It kinda bothered me, but I never had any problem with it coming out accidentally. Since I no longer own the unit, I couldn't tell you what size it was. I went to ratshack and the guy had all the tips available for me to try out.