"The meandor compression spring... or corrugated spring... is a promising design variant for compression axle springs of composite material... The middle surface of the meander spring is the... "." ...[T]he middle surface ...is the ...[i.e.,] can be unrolled onto a flat plane without stretching or tearing it. ...[A] developable surface ...in three-dimensional space and ...complete ...is necessarily ruled. This property is of primary importance for manufacturability... The meander spring... is modeled for mechanical analysis as a thin shell."