"I usually use 4mm x 40mm screws. These were not in stock so i bought the 3.5mm x 40mm instead. Got to say that for the woodwork i do i should have had these long ago. They are strong, durable and better than the 4mm personally speaking. Definately recommend to others to try these out. And for 2500 screws for just 13.50 you can't really say much to that! Great screws."