"S"Hook for MetroMax i¨ or MetroMaxQª, connects add-on units to starter units, used for end-to-end configurations (collar-to-collar connection), (2) required per storage level, also used with MetroMaxQª for right angle configurations (Use (1) M9995 + (1) Q9995Z) per storage level, NSF, Note: collar plug provided fits MetroMax i only