[TowerTalk] Screws used in Element Construction

[Garry]

Greetings all,
I am rebuilding a 17 meter beam I built about 35 years ago. At the time I used slots and hose clamps where fastening element sections together but this time I am going to use sheet metal screws. My tubing sizes will taper from 1.125" down to .625" in 5 sections per side. 
I can't find any information on what size screws to use unless I'm just looking over it. I have seen a recommendation to use hex head screws rather than typical flat blade or phillips head due to possible damage to the screw head but nothing on screw size. I also wonder if self tapping would be a better option than standard sheet metal type. 
Any thoughts will be most appreciated.
Thanks & 73,Garry - K4OR