soldering 9920 to 9xl
 

What is the best way to solder your motor to the controller "wire to wire" Should you use a butt connector and solder it , or should tou solder the wires together directly?

use 5mm gold connectors for ease of things.

Yup 5.5mm connectors are the way to go for this. Mke carries them ;)

is it possible to use 4mm connectors?
because I've got those laying around.

They won't fit the motor. The motor should come prewired to 5.5mm females, so all you need is 3 5.5mm males plugs. They are about the best and easy to solder and give great connection!

Yes you can use 4mm connectors on your 9xl and 9920 if thats what you have. They should be fine.

I never had a problem with the 4mms. technically the 5.5 connectors will handle more amps but the 4mm never heated up or anything when I used them so they were fine.

I used 4mm for a while and then switched to the 5.5 only because the Quark came with 5.5 and it was a pain having some motors/controlers using 5.5 and some using 4mm. So I switched all of them to the 5.5s. Now I can swap motors from vehicle to vehicle with no hassles. Just plug and play.

I'm running 4mm on my 7xl just because the mm esc already had them and I had the males in my box already.. seem fine to me never hot..
phil

If you solder directly You don't need a butt connector.
You can use one to make it look neater.
You can go with the 4mm plugs since you have them.