The plastic ones are not to be put through the holes in your roof, they are to be inserted into the lamp housing (square holes) so when you tighten the lens down on the roof the screws dont crack or pull threw the plastic much like a spacer.I didnt use the little metal clips just drilled the holes in the roof smaller the the diameter of the screws, throw out the supplyed screws they rust real quick and get the same ones in stainless,remember to use sealent around the holes in the roof just before you screw the lamps down and be generis on the amount you use,dont want no leaks.