What plug is this?

[agent4573]

So I just got a Powertig185 and want to wire it up. The attached picture is what I have on my wall. It says Nema-6 250V on it, but looking it up, there's a ton of different nema 6 plug types. Sorry for the crappy image quality it was a cell phone pic. It has two horizontal pins the same size and a round pin below that. So what should I be looking for at home depot tomorrow? Also, the powertig is a dual voltage option so is there anything I need to do to the welder itself to select 240 Volt mode or will it pick it up automatically?

Thanks