Rectangular steel tube bolted connection
Tube steel can be bolted or drilled and tapped if you don't want to weld. It can also be riveted but this can be tougher than welding (not talking pop rivits here but steel pins that are heated and flattened) . I believe welding is more common because there are less holes in the steel but it can be done and depending on your hole placement and wall thickness bolting can holdup and still be able to disassemble without grinding or air arcing the welds off.