This is the larger, 8.4" brake disc used on classic Minis after 12" wheels were standardized in 1984. Ref: 21A2612, 21A2612E, 21A2612MS, GBD806, GBD90806MS.
In response to complaints that some aftermarket rotors were warping quickly after initial installation, Seven has located a supplier whose product is made in a superior material.