All you needed was a straight piece of fabric with a hem and a casement to slip the hoop into. (I like the idea of turning up enough to make the big pockets--would have made a good clothespin apron.) "In those days" we ironed everything and it was a lot easier to iron a straight piece of fabric than one gathered onto a waistband. The plastic hoop went around the waist--quick and easy!

They are apron hoops. This was the first project I made in home ec in 7th grade. That would be 1954. I've been hooked on sewing ever since. Quiltingshorttimer is exactly right.
Sue

Have never seen anything like this. Everyone I knew wore the full length.

I did the same in 1965 in 7th grade--and our teacher made us use gingham so we could make our turns on straight lines.

yes , Apron hoops easy to put Apron on and off..

I didn't identify them from the pics, but I remember apron hoops. Boy, y'all got off easy making aprons in home ec. We made sheath dresses with darts and an 18 inch zipper down the back and were hand hemmed! I did learn a lot from that project though.

I don't think they are bakelite, but you can test them by holding them under hot water (running is best as I remember) and then quickly smelling them. Real bakelite usually gives off a chemical odor. There are some more definitive tests that you can do, but that's the easy one.

So how will you use them now that you have some ideas on what they are?

When new they are very flexible and you would put this in the waist band and they would just slip around your waist, easy on and easy off.