QUOTE(Mikey914 @ Aug 20 2018, 09:48 AM)
Usually screws and tinnerman nuts. The plastic is thick enough you wouldn't have to use the tinnerman but it's more durable if you do.
I transferred the pronged nuts over from my original backpad. The prongs on the nuts don't like to stay put in the plastic so used some glue before pressing them into the plastic. Otherwise, they tend to pop out when you try to screw the pieces together. The tinnerman nuts that clip from the edges would be better. I was able to screw the pieces together more tightly with the nuts than just screwing into the plastic, but like Mark says, not really necessary as the plastic is pretty strong.