[MrForbes]

I live in a small city, there are at least 4 local stores that sell 1x1x1/16" wall aluminum square tubing. But I don't know if it would fit onto your robot easily. Also, round tubes such as ABS sewer pipe will not twist, and are readily available in several sizes (ID from 1.5" to 4" is very common), and might be more easily adapted.