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Webster 1913 Edition

Noun.

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.

kingbolt ‎(plural kingbolts)

The main bolt of a structure, especially the bolt in a motor vehicle that links the chassis to the axle, providing the steering pivot.
- 1968, Charles Portis, True Grit:
  He come at me with a kingbolt and said, ‘Rooster, I am going to punch that other eye out.’