Source : Webster's Revised Unabridged Dictionary (1913)

Kingbolt \King"bolt`\ (-b[=o]lt`), n.
   A vertical iron bolt, by which the forward axle and wheels of
   a vehicle or the trucks of a railroad car are connected with
   the other parts.

Source : WordNet®

kingbolt
     n : bolt that provides a steering joint in a motor vehicle [syn:
          {kingpin}, {swivel pin}]