I'm repairing a part of my deck where the top rail came off due to warping. The #9 x 3-1/8" GRK screws that I'm using could not hold down the rail because of the pre-existing holes.

I shopped around my local Home Depot and spotted these GRK 5/16" x 3-1/8" screws which are sold individually ($1.37 each). I decided to get 3. When I screwed them in, they grabbed the wood really well.

However, there's a small problem. I would like them to be flush with the wood. Are these the type that can be counter-sunk? If so, what counter sink bit size would I use? I've tried googling but haven't really found an answer. The screw heads say 7 x 80 which has only added to my confusion.

Anyone wants to help this terrible novice? Or did I make a big mistake by using these screws?

I'm attaching 2 photos.