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


It's usually done with self-countersinking screws. The heads of these
bore a hole into the fairly soft planks when screwed in fairly hard.

I've never seen the plugs that Fred linked to, nor seen a deck installed
with those, but maybe that's what you have. Or the holes just filled up
with dirt over the 12 years?