Jim fired this volley
in roups.com:

Another will be at 10' above
grade and the opposite one, the highest, at 11' above grade.
Can anyone tell me if A500 B grade 4"x4"x1/4" tubing will do the job?

Look up beam load tables for ASTM500 grade resistance welded square
tubing.
There are many on the web, but the links are ugly to post. Like this:

http://www.google.com/url?sa=t&rct=j...ource=web&cd=6
&cad=rja&uact=8&ved=0CDkQFjAF&url=http%3A%2F%2Fwww .pirate4x4.com%2Ftech%
2Fbillavista%2FPDFs%2FHollow%2520Structural%2520Se ctions%
2520LRFD_Beam_Load_Tables.pdf&ei=H4qgU8_kEsrNsQT9r 4D4CQ&usg=AFQjCNENcs3
_ZcMBrsNCKXgrhSmJdp6cpA&sig2=kNVIcdG4-LkJez8mY_KxGw&bvm=bv.68911936,d.cWc

Lloyd