I'm new to welding and have recieved alot of helpfull advice from you guys. I got my welder yesterday. It is a Hobart 140 Mig welder. It can be used with gas or without, using flux core wire. A guy around the corner from me swears you don't need gas for sheetmetal work on the body. A local welding shop guy told me the gas keeps the welds cool enough to prevent warping thin sheet metal, like metal on a car body. First of all how do you know the guage of your car or trucks sheet metal? Is there a tool or guage for this? Second of all when filling little pin holes from small rusted areas is it necessary for the gas setup? I know from past postings that gas is needed for cleaner weld and less spatter, but the heat thing is new to me. My welder's spec sheet say flux core is ok for certain guages of metal, so I'm putting it out there to the welders amongst us, what do you guys think? Steve.