iFlyers,
I also purchased RAM p/n RAP-B-375U (bag of loose parts, no instructions) and discovered that the part that is the vertical part of the "T" is merely a long hex set-screw. You are supposed to hold the screw from rotating with an allen wrench (not supplied, of course) while you turn the ball mount to tighten it, thus preventing the screw from turning and over-penetrating and possibly damaging the iFly. I suggest filing flat the end opposite the hex so you get good purchase on the threads while the end is flush. I also made a more suitable top for the "T" (not so long & wider) and put a very short piece of tiny vacuum hose on the screw to center it better in the top of the keyhole. It's solid, works great, but I hate that it won't fit in the case (which I love) and it requires an allen wrench to put on and off.
Alas, it now appears that RAM is supplying this part fully assembled and with the "T" as one piece. This might be OK if you can bush up (no pun intended) the screw, as I did, because, as Walter says above, the top of the "T", as supplied, is a bit too long and narrow, and you might clamp it off-center too much to get a proper fit and grip. They did seem to solve the over-penetration problem. As Walter says, think cross instead of "T."
Happy landings,
Don