truck center plate
See under center plate.
one of a pair of plates that fit together and support the body of a car on a truck, while allowing the truck to rotate with respect to the body. One plate (body center plate) is attached to the underside of the car body and the other (truck center plate) is part of the car truck.
Origin of center plate
First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019