Those are aluminum. I just stuck some 1/4 by 2 inch width in a vice and hit it with the sledge to get the little angle. The T-bolts are greenhouse hardware. It doesn't take long to whittle out a couple and they are really surprisingly strong. Just like LRJoe, I pull the 4 rod holder off the front and stick it on those brackets in the sides and pull 3 or 4 cranking poles off each side during the heat of the summer.