Please don't use screws for framing, especially something like a deck. Nails are a much more suitable fixing for holding a deck together (and just about all other timber framing) as they allow the frame to move slightly without causing damage they also have a much higher shear strength. A galvanised 4” nail will hold very nearly as well as a screw with the added bonus that you can probably buy 15kg of nails (should you want to) for the price of 100 appropriate screws.
Please don't use screws for framing, especially something like a deck. Nails are a much more suitable fixing for holding a deck together (and just about all other timber framing) as they allow the frame to move slightly without causing damage they also have a much higher shear strength. A galvanised 4” nail will hold very nearly as well as a screw with the added bonus that you can probably buy 15kg of nails (should you want to) for the price of 100 appropriate screws.