flux-core is the type of wire you feed it, which is what i use. mine is set-up for gas but i havent used it. im using .035 to be exact. it comes in various thicknesses. i have used mine for 22 gauge sheet metal , up to 1/8 plate. try various gauge metal for practice to get your settings where they need to be (heat range/wire speed/technic). i did all my body welding with mine. im sure more experienced folks will chime in