What to attach slats with?

[Snickarkirre]

That's the right approach for end joints on decking, but shouldn't be necessary for fence slats. The advice to pre-drill with an oversized bit that someone gave might have possibly led you to choose the wrong bit.

I wrote that the original poster should use a drill bit 1mm larger than the screw if they choose short screws. The reason for this is that if it’s a short screw, likely not much of the screw is unthreaded (in this case about 20mm of the screw should be unthreaded), and it won’t secure the slats properly until the screw is countersunk enough that there are no threads left in the slats. How is that wrong?

 

[fribygg]

I wrote that the original poster should use a drill bit 1mm larger than the screw if they choose short screws. The reason for this is that if it's a short screw, there's probably not much of the screw that is unthreaded (in this case, about 20mm of the screw should be unthreaded) and it won't secure the slats properly until the screw is countersunk enough that there are no threads left on the screw in the slats. In what way is that wrong?

The hard school of life and basic school woodworking lessons half a lifetime ago taught me that pre-drilling, if and when needed, should be done with a drill bit smaller than or the same size as the screw. Pre-drilling should be done to a maximum of 75% of the screw's length.

There are certainly special cases and materials that require otherwise, but the original poster was asking for advice on attaching fence slats, and in post #6, you advised drilling with a larger drill bit than the screw, which I believe is directly incorrect, as it risks the screw not having enough wood to grip.

 

[Snickarkirre]

I was referring to pre-drilling only the slats so that the screw will hold the slats better if the OP uses a short screw and not what the slats are being attached to, maybe I was unclear about that. Yes, if you drill with a 1mm thicker drill in the studs/posts that the slats are to be attached to, they will hold really poorly I simply need to be clearer next time and the posts do not need to be pre-drilled at all, nor do the slats unless it is near end grain or if you are using short screws as mentioned.

 

[raveper]

It will be like a game of pick-up sticks with all the good advice.

 

[Peter2400]

It will become a real pickup sticks of all the good advice.

I'll throw in another tip then☺️
Hidden decking screws have minimal heads but hold well.

https://www.jula.se/catalog/bygg-oc...tfria-skruvar/trallskruvar/trallskruv-005157/

 

[Vermilion]

I'll throw in another tip☺️
Hidden decking screws have minimal heads but still hold well.
[image]
[link]

I'll never see the outside of the fence, so I don't care how invisible the screws are

 

[Peter2400]

I will never see the outside of the fence, so it doesn't matter to me how invisible the screws are

Then I would have used screws with large heads, like these for example.
https://www1.thomee.se/dokument/PD/PRESTANDADEKLARATION TRÄSKRUV BIG DOG C4 LOW.PDF

 

[Vermilion]

They became stainless steel decking screws. They seem to work excellently.