That is what I have.
is any oner elsew having this problem? How do you gys mount you unions to a channel board? Also what is C3? and what would padding do to help? Could I just get a power drill and drill them tight tight?
I dont recommend power tools, are you using a philips #3 screwdriver?
It looks like you have two things going one, if you say it starts and 15 and ends at 6, the biding is rotating between the disk and the board.
Looking at the picture the disk is moving, it starts with one screw mounted on the 2nd whole and one screw mounted to the 3rd hole, but end up both on the 2nd hole.
The slots on the disc should probably stat perpendicular to the channel with both screws using the same corresponding hole. both using the 2nd hole. That disc can only rotate so far.
The padding would add friction height and prevent the binding from rotating. But if the padding is too thick, your screws will be too short, and you won't be able to tighten them.