vintage 20s 30s marcel wave metal clips for permanent waved flapper bob bobbed hair curlers

We've been told that these giant metal 'barrettes' are actually clips for waving bobbed hair, 20s or 30s vintage. It seems to us that you'd need very thick hair to use these as they are, but we're not exactly sure how old fashioned permanents work. Anyway.

These are 6" long x 1 1/2" wide, all in good clean condition without rust. There's six of them in this lot, I think that would be a head full, three waves on each side.