Jagger spring

from The Collaborative International Dictionary of English v.0.48

Jagger \Jag"ger\, n. [From 4th {Jag}.]
   One who, or that which, jags; specifically:
   (a) a jagging iron used for crimping pies, cakes, etc.
   (b) A toothed chisel. See {Jag}, v. t.
       [1913 Webster]

   {Jagger spring}, a spring beneath a seat, and resting on
      cleats or blocks in the body of a vehicle. --Knight.
      [1913 Webster]