Its outdoor decking. The joists are 2x6 and was told to use a hanger on the top and bottom to prevent twisting. There is 16 nail holes per hanger (8 into the board and 8 into the joist) - 2 hangers per end of joist and obviously 2 ends = a lot of hammering!
I've used nails so far but I'm getting bored of hammering. I'll check out the recommended screws - thanks.