kingbolt
nounA vertical bolt that joins the body of a wagon or other vehicle to its front axle and usually acts as a pivot.
A large bolt connecting the fore part of a carriage with the fore axle. The axle rotates about it as a joint “when the carriage is turned.
A large bolt which passes through the truck and body-bolsters and center-plates of a carbody and the center of a truck.
Also
An iron rod in a roof- or bridge-truss, used in place of a king-post to prevent the inclined members from allowing an increase of the distance between the tie and the compression pieces.
nounA 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.
nounThe main
bolt that provides a steering joint in a motor vehicle