What is this style of picture frame called?

I have some convex glass silhouette paintings from the Benton Glass Company from the 30s or 40s. They came with metal frames, each bent from a single piece of metal with a hook on one end and a hole in the other for it to hook into. One of the frames broke, and I can’t find any information about this style of frame. The best resource I’ve found about the paintings so far is http://www.glassencyclopedia.com/silhouettesonglass.html, but it only refers to the frames as "thin metal frames".

I took this picture of one of the intact frames, opened so you can kind of see the hook closure.