The Hasselblad A12 film back is the quintessential 120 roll-film back for Hasselblad 500 Series medium format cameras (part of what is now known as the Hasselblad V System).  Unlike the original 'Hasselbald 12' roll-film backs, the A12 automatically stops on frame number one when loading and queuing a fresh roll.

The A12 fits twelve 6x6 (56x56mm) format exposures on a 120 length roll film.