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Is that also a Vittoria? If so, thats just an extender that goes UNDER the red Vittoria extender that has the valve core in it. Its a different, finer thread on the Vittorias, as you can see on your picture between the end of the red and the black extenders.
Neither the tub itself, or the black extender has a valve core in it. If you're thinking of returning it, what tub was it, and how much did you pay for it? might be interested.
Marked in red is where your black piece goes:
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What is the black valve and why won’t it inflate?