Rectangular steel tube bolted connection

Question

Is there any way to make bolted connections (T-shape, L-Shape etc) for rectangular or square steel tubes to avoid welding but also achieve modularity of the structure?

Threaded tube inserts can help a lot but i am not sure about the rigidity of the final structure because they are plastic.

Any other techniques or recommendations?

EDIT.

I interested in joining square or rectangular hollow sections. Not cylidrical pipes or strut profiles.

-For example i have found this solution that needs only two holes - one for each tube - and two threaded pieces of metal.

-Same logic for pre-drilled profiles

Another solution is to directly weld a piece of threaded metal at the end of each tube

Answer 1

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.

Answer 2

It's not square, but you might consider Kee Klamp structural pipe fittings, or similar brands.

https://www.simplifiedbuilding.com/pipe-fittings/kee-klamp

Answer 3

Google something called strut hardware. They make all kinds 'tee' and 'ell' brackets. They are very heavy duty. Good Luck.