Made of the "flexible material" Koroseal in the U.S.A in the 1940s.
Unused old warehouse find so never used, the prongs are a little corroded, but easily cleaned.
They come with their original Koroseal label still attached.
Made of shiny red vinyl, 2.5cm wide.
I have 3 sizes, each size has several holes and fits
1. 25" to 28"
2. 28" - 31"
3. 31" - 34"
4. 35" - 38"