Tein Street Basis Z Coilover Kit 2016+ Mazda MX-5 Miata (NDERC)Tein Street Basis Z Coilover Kit 2016+ Mazda MX 5 Miata (NDERC) About the Sealed Structure The top end of the shell pipe is narrowed, oil and gas are injected, and the whole unit is sealed by crimping the metal. This new approach massively shortens the production process. As a result, we have succeeded in vastly cutting production cost. Thread Type Ride Height Adjustment The ride height can be adjusted by moving the lower spring seat up or down.