1) Bolt 2) Kingpin 3) Swivel pin 
• (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.
King'bolt` (-bōlt`) 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. 
[n] - bolt that provides a steering joint in a motor vehicle
kingpin noun bolt that provides a steering joint in a motor vehicle
a vertical bolt connecting the body of a vehicle with the fore axle, the body of a railroad car with a truck, etc. · (in a roof truss) an iron or steel rod serving as a king post. Also called