Review on Heavy Duty 12Ft Double Sliding Barn Door Hardware Kit - Smooth & Quiet Operation For 36" Wide Doors - J Shape Hanger Black | SMARTSTANDARD. by Mark Lodge

Rail kit has all the parts I need to make my projects work. I would buy it again from here. But I am very confused on something and cannot seem to get an answer: I did receive the small rail connector but how exactly does it connect anything? I seem to only have one side with four small screws. The little box this came in in my big package shows that there is just a small 4-holed bar with 4 short screws and the small allen wrench to work them, but there is no back and I have no idea how to connect it to anything. What does it tighten to and how, exactly? The manual that came with the kit shows some sort of backings to this connector but those are not included nor can I seem to identify them anywhere online so far. I was under the impression that using a connector could effectively extend the length of rails by joining two together but this does nothing on its own. Can anyone please explain? I googled rail connectors and every supplier also seems to only have the 4-holed piece with the 4 short screws. No backs exist but this still does nothing for me. What am I missing? And how do I find it?