When I installed mine yesterday I think I settled on 13/64" as I also could not find a recommended size in the instructions. I started smaller for pilot holes and worked up a couple sizes. You may want to try 3/16" and if that’s too snug (I think it will be too small) bump up one size and they should go in most of the way by hand then a gentle tap with a hammer sends them home such that only the collar the top will be sticking out from the wall.
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