very old plastic shims from my father, circa 1950 ?
Econ-O-Shim is printed on them.
Black shims are 1/4" thick, red shims are 1/8" thick.
I asked to be contacted if someone knew exactly what function they were intended for,
I received the following email:
"They are for metal frames.
Glaziers use them.
I was in that line of work at one time.
you use them as shims, the screws can go in the middle of them
and they are between the frame and wall.
Example for the metal frames Wendy's food or MCD's."