Welding Tips and Tricks

Newbie learning to Mig max steel thickness probably about 3mm 1/8 inch Mig spec sheet is 40 Amp Min 150A Max - should i be using 0.8 (.030) or 0.9 (.035) wire

Machine about 30 years old that i just brought Currently has 0.9 in it

.030" wire has a range roughly of 40-145 amps - it's a great wire for your size machine.

Any disadvantage using the .035 up first

Not really, it's approximate range is 50-180 amps.