Let me also let you guess a bit
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Guess what this is. Other: What are the internal threads for?
Such rough transmission teeth:lol
It looks like a transmission sprocket, and the internal threads are used by the drive shaft to transmit torque.
Master, you are basically right. It is a coupling.
It is an internal eccentric gear, which should be connected to the gear shaft to perform non-center work, and is used for mechanical parts such as mixing and powder conveying pumps.