squarebody lca question

I was reading on another project 86 bagged and he was was talking about plating his lca with 8' i.d. tubing.

Can someone explain to me what that is and/how it's done?

Thanks!

specifically here, at the bottom of this thread.

you get a 8inch or larger pipe and you basically are cupping the lower arm. most guys do a 2inch or 3 inch cup.