I was assembling a piece of knockdown furniture and noticed the kit contained nuts with built-in washers. Because I find these to be convenient, I went to buy some for another project, but my local hardware store doesn’t stock them. In any case, they said they’d never heard of them. What are these nuts called, and where can I find them?

Nuts with an attached lockwasher are called Keps nuts. When the washer and nut are one piece, that’s a flange nut. You can find both at hardware or fastener suppliers on the Web. I’m surprised your hardware store is not familiar with these nuts. Maybe while you’re looking for these fasteners you should also look for a different hardware store.