The Collaborative International Dictionary of English v.0.48:

Kingbolt \King"bolt`\, 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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

kingbolt
    n 1: bolt that provides a steering joint in a motor vehicle
         [syn: kingbolt, kingpin, swivel pin]