ORIGINAL: cmoulder
I think you will eventually need the buttonhead screws. Mine seemed to hold well at first, but eventually there was some slippage. Another annoying little job, but once done the problem is well and truly resolved.
You don't need many screws. I used 6 on the pipe originally which is way too many. On the second set-up I used 3 and it's holding fine. 2 screws is all you need, each, on the pipe and header, about 180 degrees apart.