While this Tip shows a quick-fix to a problem with securing a toilet seat, the same method can be applied to similar problems with other plastic situations.
A toilet seat, usually with a hinged cover, is bolted to the toilet bowl for a flush system. The bolt is usually made of plastic with one end flared to secure the seat to the bowl. The problem is, very often the flared end of the plastic bolt slips right through the hole of the hinge’s base. You can get a metal washer but it would rust in no time. Anything else (stainless steel washer, plastic washer, etc) would be too much of an effort to find/buy, if at all available.
Both completed. Just a minor tip here: in a paired situation ( two bolts, two lamps, two batteries…etc.) always repair both/change both together. If one has failed, most likely the other will fail soon too.