What Red said. If memory serves, it was an M5steel torx-head bolt about 15 mm long screwed into a threaded brass insert affixed to the far end of a shouldered rubber expansion expansion nut. If nut exercised or lubricated often galvanic corrosion secures the bolt to the insert, which then spins freely in the aging/decaying rubber. You can just pull up forcefully on it to free it if necessary, pulli g it enuf to grab or else entirely out, but the rubber expansion nut will need replacing if you do this.
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