In framing the question, I can't be more specific as I have no idea (though a suspicion) about what this came from.
I have a number of them that are several different diameters from 125mm to about 300mm.
They are very thin steel (< 1mm) and each size came in a tight stack, as though laminated. They don't seem to have been glued together as they come apart easily. We have had them for about 20 years. Note the notch at 7 o'clock possibly to align or secure a stack.
I suspect they are part of some sort of electrical winding, but I would have thought they would have "teeth" on the outside.
Any ideas what they came from?
Nowadays they are part of an art project.