Square and rectangular tube is almost always done as round tube that is
run through a 'turk's head" roller (4 rollers at 90 degrees to each
other and mounted at an angle to the direction of travel) I don't think
I've ever seen a DOM tube done as a square.

1/4" wall will be done to A500 (A, B, or C) specs, not A513 specs. Most
mills will have much better actual product than the specs call for. Call
your local supplier ask what they have.

I'd suggest that you will have better luck looking for even inch sizes
in this relatively large tube.

wrote:
Does the drawing process improve square tube's twist and straightness
(over ASTM A500 or A513)? I am looking at using a 4.5"x4.5"x0.25"x13'
steel tube to mount a profile rail. One side of the tube has to be
machined to be flat to within 0.040". The less twist the better,
otherwise I must specify excessively thick walls to leave enough
material for machining. I am using the ASTM A500 twist specification
of 0.087" per 3 feet of length.

Also, does the drawing process create surface tension in the tube that
will relax when one face is milled (causing the tube to become
warped)?

Am I better off using something other than DOM tube? Low twist is
more important than strength in this application.