Start a rectangular tube part

Start a New Part. In the ribbon's Quick Features group open Shape, then Square/Rectangular Tube. The stock shape supplies the part's starting solid; it isn't the flat-part Shape Library of flanges and plates, and not a Frame Builder session. Start from a fresh document. Changing an existing part to another shape type asks to clear its features, end conditions and custom planes and resets the shape, so it's no way to resize a tube. To resize, edit the base shape's parameters instead.

Select the part root to see Part Properties and check Units and Material. Use Inches for this exercise, because the built-in HSS sizes are inch values and existing dimensions aren't converted for you if you switch. Under Features, select the base-shape entry to open Rectangle Tube Definition, with AISC Size, Width, Height, Thickness, Corner Radius and Length. Thickness is the wall thickness.

Pick an AISC Size to fill in the cross-section; Width, Height, Thickness and Corner Radius become read-only, and Length stays a separate value you set. Or choose Custom, which keeps the current numbers as a starting point, and enter Width, Height, Thickness, Corner Radius and Length yourself. Leave each field to apply it, then look at the solid. Width, Height, Thickness and Length must be positive, and the wall must be less than half the smaller outside dimension. Passing that check doesn't guarantee every corner radius can be built.

With Custom selected, Save Custom stores the cross-section under a name you choose: Width, Height, wall Thickness and outer Corner Radius only, not the Length, features, setups or any program. The name must be new: not Custom, not an existing saved name, not a catalogue size. Delete appears next to a saved user size and removes that library entry after confirmation; it doesn't delete your part.

Save the part as a .gcmprt file. Saving a custom section isn't the same as saving the part. Reopen it to confirm the section and Length before you build a job on it. Holes, end treatments and operations are added in their own workflows and organised in a setup. A tube on screen has no cutting program yet, and a linear stock job will still need the part's posted companion file.