I have an old bag of toroids, I've had them for 25 years and I have no
idea how long the previous owner had them before me.

The label on the bag says:

40/50 mix

They are about 15/16" OD, 9/16" and are 5/16" thick. They are green
(ID/OD and one side) and yellow on the remaining surface.

I would like to use them in a frequency sensitive application, so I
really need to know what a '40/50 mix' means.

I've googled, got nothing. When I included "toroid", got nothing even
close when I left it out I got things like recipes, motor oil spec's
etc.

I think the 40/50 mix is the old method of grading the material, but I
can't seem to find anything about it on the web.

Any idea what this mix is good for?

Thanks,

T