The XT-60 DC connectors are suitable for low current DC applications with up to 30 Amp of continued current.
See the 4 - 6 - 8 rule for DC currents
You can solder the 6 mm wires (6 x 4 = 24 Amp) or the 4 mm wires (4 x 4 = 16 Amp) to these connectors.
Check the DC XT-60 connectors here.