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The Spyderco Fine and UltraFine are made from exactly the same material. The only difference is in the factory lapping. That is why Spyderco specifies that lapping the hone voids any warranty.
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Your experience does not jibe with mine or that of others I have encountered here. The "factory" lap of the Nortons, especially that of the 4k, is considered to be awful in that it is not flat. ...