This is a pair of black U-Hook Cross Bar Holders for Super Clamp from Impact. They are meant to hold up the cross bar of your background support system. The hex head studs on the U-Hook Holders fit neatly into your two optional Super Clamps that are then connected to your background system uprights. The Impact U-Hooks are made from solid aluminum.
Difficult review to write & explain. Purchased 4 Super Clamps assuming there was a cross bar hook either included or integral to the clamp. There was not so I purchased the U-Hooks by the same manufacture again assuming they would be compatible, they are not. The U-Hooks are well made, of a good gauge of steel and nicely finished with a matte black coating. I should have done more research before making the purchase. Ultimately I'll figure out how to modify and make the U-Hook Stud work for my intended use.
The Super clamps are standard Manfrotto, which attach to my Pole cats. The folks at B+H were very helpful when we discovered that NONE of the U hooks fit into the super clamps, even the Manfrotto variety. The impact U-hooks were a bit cheaper and I have had good luck with Impact in the past so I purchased these, knowing I would have to file them down, which you can see in the photo. Its curious that all of the U-hooks were too wide to fit into the notch in the Super Clamp.