Hollow brass box section has a square outer profile and an empty bore. Three sizes are stocked — 1.6, 2.4 and 3.2 mm in 305 mm lengths — and they step up so that the smaller section slides inside the next one, which is what makes them useful for extending legs, telescopic props and accurately nested joints.
Against the styrene equivalent, brass gives a thinner wall and will take a load without flexing, so the finished part looks right and still survives handling.
Brass box section will not bond with solvent cement. Solder it, or use cyanoacrylate on a keyed and degreased surface. Cut it with a fine-toothed saw rather than nippers, which would crush the thin wall before the cut was through. The rest of the metal shapes, from solid rod to angle, sit in the brass profiles, and round hollow stock is under brass tube. If the joint is going to be solvent-glued and nothing has to carry weight, styrene square tube is the simpler choice.
