comments:
As others say: it's a rivet, you have to deform the plastic with the pliers in order for it to hold. So try that. Side note: in my experience your press is of a difficult style. With the sort of scissor style you have, the surfaces hit the rivet at a slight angle and only become level wih each other as you press tighter. This makes it easier for the rivet to go awry. There is another style of press where the surfaces come straight from above, I find it works much better. Random link off google to demonstrate the style, I don't endorse this brand/specific product: https://www.walmart.com/ip/KAM-Professional-Fastener-Snap-Pliers-300pcs-20-Colors-T5-Snap-Plastic-Buttons-Kit/1079346703 (I just have a cheap set bought at a local discount store. Works great as long as the dies are screwed in properly. Works awful if they're not, lol.)