If I remember correctly, the plastic ones have a slight shoulder that gets pressed into the hole of the fender first. Then the emblem pin gets inserted which kinda swages the plastic out to hold it in place. They are a pain to install but when done right they hold well.
That was what I did but I think the holes in the fender were too large for the clips. The holes in the fender were right at 3/16 which fit the barrel nuts just fine. The clips seemed like they needed a smaller hole. Could be the clips were not made correctly or maybe my fenders were drilled for barrel nuts. I don't really know and I'm not sure who would know. I called a couple of folks but nobody had any dimensions or hard facts. That is why I just bought both and tried them. They were only a few bucks each so it I didn't mind trying both to see which worked the best.
