The connectors are called Tube Clamp: fits 1-1/2" ID, 1-3/4" OD x 0.120" Wall Tube. Two Pieces w/Hardware.
Now I know some will comment that there could be more bracing, triangulation etc. The instructions that I gave the Fabricator were: "Primary Objective is to keep the roof from caving in, specifically the A-pillars. I don't care about saving the truck or its sheet metal." and " When you get to three thousand dollars then STOP, that's all I have to budget."
Now that its all done, he cautions me: " Now just because you have a cage that doesn't make you an invincible rock buggy, this is a SAVE YOUR LIFE ONCE cage". The expectation , if I ever do roll it over, is to rebuild it.