When I say this is rare, what I actually mean is that this might be the only one out there, especially in this condition. I've never seen another M adaptor with the split mounting feet to attach to a 600 SE, it might be a one of a kind modification from the original owner. This is one of the newer 6x7 rollfilm backs with the cranking lever instead of the knob. Looks like it was never used, just sat in storage. There a few external scuffs, probably from being moved around in storage since it was made sometime in the late 80's. Internally it looks incredible, still has the original packaging paper and the instructions! These film backs are renowned for having some of the best film flatness in the 6x7/6x9 format. Everything on this works like new, it has the 120/220 pressure plate that you can flip to switch between the two. The only downsides are that the foam seals seem to be long disintegrated, and the dark-slide shows some minor wear. The seals can easily be replaced with some black wool yarn or craft foam. I'm guessing the dark-slide was swapped out from an older model that was actually used. This film back would be perfect for you if you've invested in a great Polaroid 600 SE system but are now limited to slow ASA 100 film since it's the only kind still in production. Get this and you can shoot fast again with Delta 3200 or the likes. Given the rarity and condition of this item, I'm looking to get $300 + S/H from Ohio. If that sounds steep, I'm always open to reasonable offers, so message me and make me an offer.