You can use both 0.6mm and 0.8mm diameters in the R-Tech MIG 181. We get excellent results when we use the following -
For anything 2mm and below, such as car body work, we would recommend 0.6mm wire thickness. This is because the wire requires a much lower amperage to achieve briliiant penetration and prevents burning holes in the work piece.
For anything 2-3mm and above, such as chassis work, steel fabrication we would recommend 0.8mm wire thickness. This wire thickness is a fantastic all rounder as it suites many of the users requirements.
Our machines are fitted with a double grooved roller to suite both 0.8mm and 0.6mm wire. Simply unscrew the retaining screw from roller, turn the roller around to match the wire diameter and re-install the retaining screw.