A holder for the blades of the "modern house basis mandoline":
e.g. https://www.kitchn.no/nettbutikk/kjokkenutstyr/kjokkenredskaper/46180043/
it works, but it was a quick design and print. so roundings do not fit totally those of the parts.
unfortunately i cannot upload freecad files here....
i printed it with the back facing the bed, so there is only a bit of support for the front of the side holders.
The author hasn't provided the model origin yet.