I got the bf screws from modmakers
Fat Daddy Vapes Bottom Feeder 2.5mm Posi Contact With Hex Hole
Unfortuately, they haven't got any in stock now. I'll hunt around later and see if I've got any spare.
I think I used a 1mm drill bit.
I'm sure you'll do a better job than me as I'm shite at all this.
cheers
Gaz