In a post back in 2021, I highlighted some interesting artifacts discussed in a 2001 article by Susan Wood. It’s a fascinating piece that focuses on two decorated ivory plaques with curious sets of holes found at Pompeii. The image below from her article reproduces the front and back of one of these plaques:
Wood makes a plausible case that these pieces were parts of a device for holding open papyrus rolls. She pointed to plaques of similar shapes and sizes in Cambridge and Nîmes, which are preserved together with sets of rods that fit through the various holes in the plaques:
I recently had a chance to see the Pompeiian examples in person. Only one of them was in Naples, tucked away in a nondescript case in a corner. The other one, however, was part of a traveling exhibition at the Capitoline Museums in Rome. This one was in a case that you could actually walk beside and around, and it was interesting to see just how curved these plaques are. This is something that Wood noted in her article, describing the pieces as having convex and concave surfaces. I think that, when I saw the images above, I failed to register just how pronounced this curvature is. It’s a a bit difficult to see when viewing these objects from the front:
But looking at them from the side gives a better impression of the way that they curve.
I’m not sure how this curving surface would affect the way that these objects might function as the ends of devices that would have held papyrus rolls. One of the arguments Wood makes in favor of this interpretation is the idea that the ends of the papyrus rolls would rub against the plaques: “The more abraded concave surfaces must have been the inner sides of the plaques, which came in contact with the edges of papyri” (p. 32). But, if the plaques were curved, would the edges of papyrus rolls actually have much contact with the plaques? I note that the replica model pictured in Wood’s article seems to have been made with flat plaques like the Fitzwilliam example, and at least in the image provided, the mock-up roll only seems to be touching one of the two plaques:
If these plaques were curved, the roll would seemingly just touch the outer edges of the plaque. I wonder whether such a scenario would be consistent with the abrasion patterns that Wood mentions on the inner surfaces of the plaques? I didn’t get a sufficiently good look at the insides of the plaques to tell. I would be interested to see a replica of one of these devices in action.
Variant Readings 
The disposition of square and round holes in the Pompeian plaques are identical to square and round holes in the Fitzwilliam ones, so must be the same kind of object. But the Fitzwilliam ones have two additional knobs at the top of each plaque, which have no apparent purpose if the object was a roll-holder.
Your lowermost photo, showing Susan Wood’s reconstruction, is completely unconvincing to me. I cannot see that the contraption is serving any useful purpose: it neither holds the roll flat nor, apparently, prevents it from rolling itself up unless the reader holds both ends of the roll.
IF this really were a roll holder, it seems much more likely to me that the roll would be placed underneath the rods (not resting on top of them), such that one column of text could be read between them. In such a configuration, the object would at least keep the roll from rolling itself up, and would leave the reader’s hands free. But this still does not explain the knobs on the Fitzwilliam version. I thereore personally think it likely that the object served some other purpose.
Thanks, Peter. Yes, I think all of these are the same type of object. The Pompeii plaques also have holes in the upper corners (hard to see in the images in this post; a bit easier to see here: https://commons.wikimedia.org/wiki/File:Naples_Archaeology_Museum_%285914752300%29.jpg). It seems possible the holes in the plaques from Pompeii may have held pegs similar to those in the Cambridge example.
Now that I look at the Susan Wood article to which you linked, and I see her fig. 7, her hypothesis seems a bit less implausible to me, but I am still very skeptical.
Part of the problem is that the contraption seems for too over-engineered to perform its required function. To hold a roll open and stop the ends rolling themselves up, all that one needs is a suitable weight (such as a smooth pebble) for each side!
I also wonder if the iconography of the carving ought to be a clue to the object’s function …