On 04/06/2021 14:27, Suzanne Clarke wrote:
Hi

We are replacing some decking and have the boards delivered. The previous deck was installed by the builder's chippie about 12 years ago. We have started taking the old boards off. The screws, which were invisible before, start half way into the plank and then screw into the base. How on earth is that done?

Thanks
Suzanne

Have the holes been plugged
https://www.woodmagazine.com/woodwor.../joinery/plugs
or simply driven into the board using an impact driver?