Square tubing that fits inside a larger square tubing

[verbotenwhisky]

There are a bunch of YouTube vids with ways to remove the inside weld flash.
If you need a fairly good fit Get the nominal sizes. ie 2" x 1/4 wall and then a 1.5" x 1/4 wall for the inside.
Remove the weld flash on the outer tube. Or grove the inner tube.
Machine 2 sides of the inner tube to get the fit you want.

I usually buy seamless tube.

 

[Charles scozzari]

In regards to the radius of the square tubing there is absolutely a difference in the country of origin. U.S.A., Canadian and Chinese all vary in the radius of the steel. It starts as a round tube and is forced into the square shape and the forms vary. Where the seam is varies. The supplier I use handles Canadian Steel and is constant.

 

[RandyM]

They call it telescopic tubing. McMaster Carr sells it.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[akjeff]

If you go with the nesting square tube such as in you photo, do yourself a favor and locate the locking set screw in the corner, and pointed at the opposite corner, not on the side as in the photo. It will force the inner tube into the far corner, and support it in two planes rather than one. Will be far more solid.