HF bender is great for these. But if you just have a couple to make, you can just make a little jig on a table. All you really need is a piece of 1" to 1-1/2" round tubing, then a pin or bolt a couple inches away. Doesn't matter where. Then just but the bar between the two and bend around the piece of round. 3/8" is very easy to bend, 1/2" is quite a bit tougher to bend (relatively speaking).
It's very important that you bend the bar right in the middle so the ends touch almost perfectly. Otherwise it's a real pain to get them to be straight. I don't make very many of them, but I found it to be a huge time saver to cut the original length 4" long, bend around the center, then just put the bent piece in my saw and cut the whole thing to length. Then the top angle brackets I get laser cut. I buy a couple hundred at a time, so they're like $1.90 each. I'll sell you some if you want. Just pay what I paid plus shipping. Or you can just cut a piece of flat stock into a square, that works too. Make sure it's at least 4" flat stock. 5" is preferred.
