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I was thinking that the metal mount looks like a casting that might have had Tinnerman nuts which look more like the lower photo slipped over the big holes. That way the manufacturer does not have to drill and tap the casting and the Tinnerman can move around a bit so alignment does not have to be very precise . Then typically they screw into the Tinnerman nut from the opposite side in your photo with a screw that has a large diameter head to spread the forces so the plastic will not crack. The type of Tinnerman in the lower photo has a shoulder that slips into the plastic part and prevents you from over tightening since you can only tighten to that shoulder.
Your photo seems to show a Tinnerman nut attached to the plastic and the screw goes in from the casting side.
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