Wonder what screws are suitable for different subframes for decks?

We had a customer ask if the decking could be fixed to steel framework. The best way to do this would be to fit treated timbers to the top of the steel and use the brackets supplied with the decking to fix to those timbers. This is easier than having to make the correct size pilot holes to fit 2 brackets every metre in every bearer and buying screws that will self tap into the steel. Also the holes in decking brackets are designed for standard sized screws and specialist steel fixings would not fit them