Unistrut is a universal strut used in construction for all sorts of things. Most typical size is the 1-5/8" X 1-5/8" although it comes in other sizes thinner and thicker but all 1-5/8" wide.



This site says uni-strut is like legos and I agree. There are so many different fittings available. I made my bike hangers in my garage out of uni-strut with the rollers fittings and some hooks. I pull my bikes up into the rafters with a pulley system and rope.



Oh and did I mention is is prety darn expensive? That is why I quickly forgot about buliding a whole treestand out of them. But I have always thought that a long slotted section would be nice along the side of a ladderstand's ladder as a part of fall protection that you could adjust the catch little by little as you go up or down.