I am trying to install these hooks to hang some plants. https://www.amazon.com/gp/product/B08BKSXSMZ/
They say to use a 15/64 drill bit to pre-drill when using the wall anchors. However, I will be installing into a ceiling stud. So I don't need the anchors (I think). How do I figure out what size drill bit to pre drill with? Do I just use whatever is small than the screws?
Alternatively, should I just go and buy my own screws since they will likely be better quality?
Here is a DIY method to determine the pre-drill size.
Hold the screw and find a drill bit and hold it over the screw (parallel) that visually covers just the body (the inner part) of the screw.
You must fully see the screw threads on both sides.
Next choice depends of the hardness of the material you drill into. For a soft material, use the next smaller drill bit.
Alternate "empirical" answer: take a drill bit that is about a quarter of the diameter of the largest part of the screw (either the straight part just under the head, or the threads themselves) and use that.
Drive the first screw. If you struggle to turn it, drill again with the next size up. This method gives you the right size of pilot hole regardless of the type of wood you are drilling into.
Like STS1SS said you really could get away without predrilling at all since your chances of splitting a joist/rafter with a screw that size are very low.
However I normally still predrill any non self drilling screws. For pine I will use basically Ruskes method but I will go 2 or 3 sizes down not just 1. The dimensional lumber in your ceiling is going to be either pine or fir and they can be very soft so if you drill too big of a pilot hole it can be very easy to strip the hole out.
I think it's also worth noting that the size of the base plate on those hooks will make it difficult (not impossible) to get all 3 screws into wood. It looks like if you can perfectly find the center of your stud you can easily get 1 screw in the middle and then drill the other two inward at an angle to ensure they bite.
Personally I would line it up so that two screws go into the center of the stud and the third screw goes into a drywall anchor. If you angle the screws into the plate they wont sit flush when tightened and might stand out.
If you're going to attach to a ceiling joist, don't use those hooks you linked. It will be significantly easier and at least as strong to use a hook with a single screw into the center of the wood.
What Ruskes said...
But to directly answer your question; the screw size recommended in the docs is for the drywall anchors. If you anchor into a stud, you don't really need to pre-drill. Pre-drilling serves a couple of purposes: first to prevent the media you screw into breaking out, and second to provide a good surface for the drywall anchors to gain purchase (grab). You aren't using the drywall anchors, so you have to consider the first reason. Because you aren't worried about breakout (tearing the stud) it becomes unnecessary.
Don't worry about it.
