Many times you will need to draw a square line on sq. & rect. tubing. As the wall thickness increases on these, so does the radius on their edges, most squares will not extend far enough over the side to pick up the flat part of the other edge. A couple of methods that I have to found to deal with this are as follows: take a piece of 10GA. or so sheetmetal and shear/or cut it into a rectangular shape, at one end of this rectangle form up the edge to 90 degrees with the leg length being around 1 1/4" to 1 1/2". You can use this to lay the short formed leg against the edge of the tube and draw lines along the edge that is 90 degrees to the short formed edge to make your square lines on the face of the tube. Another method uses a modified version of carpenter's stair gage sets. These are the small brass set blocks that can be attached to carpenter's squares for laying out stairs. A modified version of these are much longer in their body length and can still be attached to one edge of the carpenter's square. They can then be laid against the edge of the tube steel and a line drawn across the tube along the other edge of the square. I'm sure there are many other methods, these are just a couple that I thought I'd throw out there. Regards, aevald