There are several parts that make up the skateboard trucks.
The axle is the pin that runs through the trucks to which the wheels will attach. The hanger, usually made of metal, is the largest part of the skateboard truck that is somewhat triangular in shape. The axle runs through the hanger. The kingpin is the large bolt that holds these parts together and fits inside the skateboard bushings.
Skateboard trucks are the metal T-shaped pieces that mount onto the underside of the skateboard deck. When selecting skateboard trucks, the width of your truck axle should closely match the width of your skateboard deck. The truck size can be measured by the width of the hanger or the width of the axle. Every skateboard requires two trucks.