Good Afternoon,
I had a chance to acquire some 6-2 w/g and would like to know if this is okay to wire my 50 amp plug to my welder? If this is okay to use; where would the bare ground wire be connected in the sub-panel. If it is suppose to be the common, would it be wired to the common strap in the sub-panel or would it be attached to the ground strap. I know they are not connected in the sub-panel, only in the main panel. Or should I try to sell it and acquire some 6/3?
Thanks,
Bob

There is NO "common". There are hots, a neutral and a ground.
Your 240v welder does not likely require or use a neutral. 6/2 w/g cable is perfect.
The ground wire goes to the ground bar.
Use the black and white as your two hots. Just mark the white to another color like red or black with a permanent marker.

Thank you, everything else I have wired 220v was always 2 hots and a common. This wire is romex which is what I am using in the walls on my shop, but I was confused with the bare ground and not a wrapped wire for the common.
Thank you again for you prompt answer.

Bob