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Double the grit means double the numeric rating: 2 x 1k = 2k, 2 x 2k = 4k, 2 x 4k = 8k, etc.

I haven't seen a test of this, but I don't think these stones warp much. If they were 3 feet long and you stood on them, yes, but at 8 inches with knife-sharpening pressure, I doubt it. Further,...

You didn't say what you use for lapping, but I assume it's one or more of the DMT plates. If so, these are not much larger than the stones you're lapping, so you'll inevitably have some parts of the...