I lost one of my seat hold down nuts awhile ago and figured if I replaced it with an original I would lose it again eventually. I picked up a couple of drawer pull knobs for .99 ea. They are all plastic and are not threaded. I just happen to have a 6mm tap so after drilling them(5mm or 13/64") I tapped the hole in the knob. It has been on there quite awhile.It makes removing the seat a breeze and are easy to check and give them a quick twist if needed.
Keith