ill have to measure to be sure, but id say 1/2" metal. They seem pretty robust, but I doubt I could hang on them freely like they advertise... tho I havent tried lolWhat diameter is the frame bars approx l, it's obviously a sturdy with someone hanging off it lol, the frame diameter is a big deal imo, I've had tents that near buckle with a good fan and filter so a sturdy frame is a must.
Ive got a Timber Redwood, 6" exhaust fan and carbon filter hanging in one with no issues at all. Im in the process of setting up my second mars hydro 4x4 tent this week. maybe ill give it a hang and report back lol