Yes, Brockett would be correct, the Monolock boxes (smaller, light duty) will normally come with a generic plate which is fine if you have some sort of rack on the back of the bike.
The Monokey are heavier duty and will generally require some sort of bike specific adapter mounts or rack and there are various plates then, from the old wingrack setup, to the simple old semi universal M3 plate, the newer M5M and the M8/M9 Alu plates.
I've got an oddball M11 tubular plate I found in the bin in Thunderroad years ago.
Loads of different setups - I would try the Givi bike configurator on their website to make sure your getting something suitable and correctly fitting for the bike.