One way to hold swivel: a pin stuck through two things so that one of them can spin and the other stays put. Everything about the word comes back to that pin. The place never changes; only the facing does. Put the pin under a chair and the chair swivels. Put it in a dog lead and the lead never twists. Imagine the pin inside a person's waist or neck, and you get someone swivelling round without taking a step.
From the word’s history
Wiktionary derives swivel from a form of Old English swifan, to revolve, plus -el, an instrumental suffix — literally the little thing that turns. That is why the part, not the movement, sits at the centre here.
來源把 swivel 追到古英語 swīfan（旋轉）加上表示器具的字尾 -el，字面就是「讓東西轉的小玩意」。所以這裡把零件放在中心，而不是把動作放在中心。
Wiktionary entry for swivel: From Middle English swyvel, from a derivative of Old English swifan (to revolve), + -el, an instrumental suffix — as supplied in the evidence packet
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