Wont make much difference for what you want to do, but 97.5% Argon and 2.5% CO2 or 98% Argon and 2% oxygen, the latter will look more dull due to surface oxidation. But like I said, most exhaust places get away with using light mig gas (93%Argon 2% oxygen and 5% CO2, the welds will be more prone to cracking though)

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R H Davey Welding Supplies. I sell new and used welding equipment in the Hampshire area. I take on welding jobs in the evenings, ally casting repairs are one of my specialities but I can weld pretty much anything. PM me with your requirements.

Some of my services: (See my for sale threads)
Engine mount/chassis repair
Solid Beam Mounts BACK IN PRODUCTION
Harness bars