Some folks call them ribbon type springs and others call them Zig-Zag springs. Ford started using them in the early 50s. They are easier to find than good coil type springs for seat boxes. They used stabilizer wires or cord to help them maintain their in line shape. Over time, the stabilizers break and then the springs really start to suffer to include breakage. Make sure they are stabilized with wire or heavy duty cord if you rebuild or replace your set.