swivel joint

from The Collaborative International Dictionary of English v.0.48
Swivel \Swiv"el\, n. [AS. sw[imac]fan to move quickly, to
   remove; akin to Icel. sveifla to whirl, shake, sv[imac]fa to
   ramble, to turn. See {Swoop}, and cf. {Swift} a reel,
   {Swift}, a.]
   1. (Mech.) A piece, as a ring or hook, attached to another
      piece by a pin, in such a manner as to permit rotation
      about the pin as an axis.
      [1913 Webster]

   2. (Mil.) A small piece of ordnance, turning on a point or
      swivel; -- called also {swivel gun}. --Wilhelm.
      [1913 Webster]

   {Swivel bridge}, a kind of drawbridge that turns round on a
      vertical axis; a swing bridge.

   {Swivel hook}, a hook connected with the iron strap of a
      pulley block by a swivel joint, for readily taking the
      turns out of a tackle.

   {Swivel joint}, a joint, the two pieces composing which turn
      round, with respect to each other, on a longitudinal pin
      or axis, as in a chain, to prevent twisting.
      [1913 Webster]
    

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