It is 1.25 inch schedule 40 grey plastic pvc electrical conduit. I drove 2 inch pvc into the ground then slid the hoops in them. Everything is secured with carriage bolts. I mostly followed this tutorial here but i would suggest painting the hoops white to increase the life of the plastic. I never got around to it but plan to this fall.
http://www.fiddleheadfarmers.com/fhf...eenhouse-plans
I am likely the worlds worst carpenter ever so I think I am going to re-frame my ends but the rest is super simple.