Mig gas bottle.

[birchy]

Probably a bit late, but I'm a C&G qualified welder. For home-use MIG, I use CO2 without any problems at all. A lot of people say "don't use CO2, too much spatter, etc" but you'll find that 99% of them have never tried it! You will get better penetration with CO2 than Argoshield and only need around 5LPM gas flow. I used to work for one of Europe's largest steel fabrication companies and we used nothing but CO2 about 20 years ago. For home use, you can get CO2 from any gas supplier (or a friendly pub landlord!). I paid £10 for a 9L bottle about 5 years ago. The other option is to get Argoshield from an Adams Gas outlet. I've recently got a 9L bottle of pure argon for my TIG set. It was something like £55 deposit on the bottle and £50 for a refill. Personally, I will not pay bottle rental because these little blighters last for years and I do quite a lot of welding.