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All Shimano centrelock rotors I've ever bought have come with a lockring. I've got at least 4 of them just sat in the drawer, never used. Even though I don't have thru axles, my cassette tool doesn't clear the QR adapters on DT Swiss hubs, so I have to use the bigger lockring. No bother as it looks much nicer than the cheap one they chuck in with the rotors, but it is a waste of metal / money to put that extra lockring in.
Rotors aren't sold with lockrings are they? I thought it was the hubs that included the lockrings?
My SP was in that situation so I bought the little kit thing that had the bigger lockring included.