There are 3mm connectiors & 3.5mm ones. Not sure who though that was a good idea. I can't tell them apart just by looking. I made a decision to just use one size & I don't even remember which one I chose, I just bought a bag full of them. Now whenever I get something new, the first thing I do is test the connectiors to see if they are the correct size for me. If not, I'll switch them out. This makes field much easier, just swap out the failed component & keep on flying.