Separator for Legrand Batibox electrical flush mounting box (https://www.legrand.fr/catalogue/boite-dencastrement/boite-a-encastrer-ecobatibox-profondeur-40mm-pour-plaque-de-platre-2-postes).

Usually when buying a 2 or 3 spots box it comes with a separator (cf picture #3).
it was missing from my Amazon order so I decided to create a model.
It is more longer than the original one, coming up to the electrical plug case.