A ladder frame has two rails going front to back with smaller rails connecting the two so that it looks like a ladder. A front solid driving axle is mounted on leaf springs. Tandem (two axles together) axles are mounted differently. They have leaf springs and arms to hold the axles. Some have the spring over the axles. Some have the leaf springs below the axles. A few extra-heavy-duty models use a simple but strong walking beam type.