Lee in Richmond

My husband bought a 'lot' of old Singer feet the other day, including a big old buttonholer with cams, and misc. other stuff. Two feet had part numbers, which turned out to be for a featherweight. A couple of others I identified from photos on eBay.

The one below, plus a random piece that came off something else unidentified, has me stumped. By the way, the ruffler/pleater foot is a work of art, but how does one learn to use it?