::There is a bit of a problem here. The center plate on a truck is not a part that can be separated from the truck bolster but is an integral, inseparable, part of that bolster and can therefore not be illustrated by itself except perhaps as an enlarged detail of the bolster. The bolster usually is a casting and the ring shown on the illustration is part of that casting. If the bolster is a weldment that ring is welded onto the rest of the bolster and the round flat space within that ring is called the center plate. I have started Truck parts. More later.