Thanks for the replies – very useful.
Whilst we’re on the subject of screws, Joe rightly says that if you need to get a nailed down board back up it’s quite difficult, (or words to that effect 🙂 ). Don’t you find it’s almost as difficult to take up a screwed down board ? We used to use the green decking screws and once they’re in for a few days, (let alone months or years), they’re almost impossible to extract without the head burring or the screw snapping. The Ecodek screws are equally difficult. I said we were installing some Ecodek recently, well we had to take up some boards on a step a few days later and we only managed to get two screws out ! The rest burred no matter how careful you were.
I must have put in tens of thousands of deck screws, if I’m the only one to find this, please tell me.
p.s. Maybe the screws you’ve all recommended will avert this particular problem.