4mm's Between Motor and ESC?
 

I want to install connectors between motor and ESC, from what I read it seems they should be 4mm on all three wires ... which brand/model/type should I be using? .. smaller the better I would assume but I want it to be as little resistance as possible? 13.5 and 17.5 motors, Hobbywing spec (60 amp) ESC and 2s lipos if it matters .. thanks!

I honestly think these things are made to be more important than they are. I used to run great planes 2mm bullet connectors on my motor wires/motor. Never noticed a difference since switching to hardwiring. I've also ran 16 ga wire for a summer and not had a problem. Sure bigger is better, hardwiring is even better, but they will all work. I prefer hardwiring, but only since buying a nice soldering station that makes the work easy to do. Honestly brushless motors are so little maintenance, it's not really a bother to just leave them hooked up and unsolder them now and then to clean them out.

It doesn't matter which bullet connectors you're using. Lots of people make and sell them including HobbyKing. I've used HobbyKing bullets with good success. But it's silly to order bullets alone. So see if you can get them from the store where your next RC order is placed.

I use 4mm connectors on my HW SC8 120 amp esc running motors that range from 2150kv up to 3500kv on 2s,3s and 4s without issue.

I have been running 4mm bullets forever. From 1/10 to 4s powered boats. I do prefer the non cage type castle ones though.