The screws I used are size 4-40 with an oval head as short as you can find them in stainless steel. I typically go to Ace Hardware for screws. I'll drill the holes in the aluminum using a drill bit slightly smaller then use a 4-40 tap from my Harbor Freight tap and die set. The SS screw is harder steel than aluminum so it's possible to use a screw to tap out the threads by working the screw in an out but a real tap is easier. The screws can be ground down shorter using a bench grinder or a file. I already owned a bench grinder, tap and die set, files, drill bits, etc. so this...