16ga = 0.0598 black pipe schedule 40 3/4" wall is 0.113"
Of course you could use the sq 1" x 16ga if in your design you reinforced the tube, but if you like your butt (hope that's not too racy) use 3/4" black pipe.
You may even consider using 1" black pipe. The wall on 1" is 0.113.
Black...