Sam, on my boat the holes into which those self tappers fitted were of the sort of size where you could stand back ten feet and throw the screws in !! I don't know for sure why they were so enlarged, but in hunting for the source of the leak that was resulting in the inboard aft corner of the mattress in my starboard cabin getting wet. It turned out that water was dripping off one of the screws and on to a wire which ran forward descending slightly until it was just inside the area where the steering cables were. Then the water dropped off, and worked its way through the poorly sealed joint between centreline bulkhead and the plastics that surround that area, and on to the corner of the mattress. Since then, no further problems. I might have used rubber grommets rather than "O" rings, but either will do. Tightening the bolts can be tricky if you are on your own, but not impossible 👹