From the manufacturer:
This wire diaphragm will fit all classic Minis built between 1960 and 1993 (before the twin-post headrest seats were introduced). Originally, a one piece moulded rubber item was used, however these are no longer available. We offer this wire and cord item as it superceded the rubber diaphragm and performs exactly the same job. It is supplied with the necessary springs to hold it in place on the frame. Ref: C708.