[Shop-talk] MIG - CO2 vs Argon

[Bob Nogueira]

 I've been using C02  with my MIG as I  have only welded  steel. My next
project will be in aluminum so I figure I will need to switch to argon.  
Questions 
Are the fittings for argon and CO2 the same? 
Are the Argon and CO2 bottles the same? 
My supplier does a bottle exchange for refills, will they generally allow
you to switch from one type of gas to another on a bottle exchange?
And, What is the price difference between Argon and C02?

Thanks 

Bob Nogueira