Some kind of tool

[dryheat]

I picked these up at a sale years ago and have never figured out what they are for.

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[Doco Overboard]

You fill them with lapping dust and use them to hard fit parts.
I bet one of them is made of cast iron.
If they have been used a lot you may see them worn some instead of perfectly flat.

[bruce]

Wow! I thought they might be something from the printing trade. Sincerely. bruce.

[PWC]

When making astro telescopes, you cast similar looking 'laps' out of pitch and use successively finer grit to grind the mirror to shape, then jewlers rouge to polish.

[dryheat]

I knew some one here would know. I thought they might be some kind of "sharpening stone".
The back side of one of them looks like it got some use. They all seem to be steel,going by; they seem heavy and solid, where cast seems lighter to me(no real education on that).
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