Standard Size for a Toolbar?

[Spudland_Dave]

Started a welding class last night...I can weld flat beads with no issues, but out of position is a whole other story...
Anyway, I was thinking of making a toolbar that I could use for anything...mutliple shank subsoiler, ground drive planter units, disc hillers, etc...
Is there a "standard size" for the square tubing...I was thinking of 4" Tubing... but I've seen everything from 2x2 thru 4x6....what would you guys reccomend?

 

[AndyinIowa]

For my toolbar design, I am using 2x2 tubing. I have a BX2350, so don't need a large toolbar.

IowaAndy

 

[kennyd]

My only "toolbar" is a receiver hitch...built with 2x2x3/16" tubing and 2x3/8" flat stock.