Giantkiller

I was looking for an answer to solve my bedliner problems. I just bought my first truck. A 2014 GMC Sierra1500 but it was missing a few things. One of those being a bed liner. I found one used on craigslist without hardware to mount it or these plugs. I ordered some plugs from GM but to my dismay they only fit the lower tie down holes. I was glad to find the answer here for the right size and the right type (soft rubber) for the upper holes. But the larger covers I have also came with the mounting screws for the bed liner. Interesting screws of various sizes with a sleeve near the head that prevents the screw from fitting tight against the liner and the bed of the truck. While the fasteners were a nice surprise the lack of instructions for them were not. I really can't tell which size goes where on the bedliner. Some are larger than others and the tailgate already has screws in it and don't want to strip the threads out putting the wrong screws in. Should I use these or use something else all together?