The invention relates to an assembly for loading parts to be treated into a single-side or double-side treatment machine, comprising—a part holder in the form of a plate for holding at least one part to be treated, comprising a second side and first side, said first side being flat, and said part holder delimiting at least one through-hole forming a cell for housing at least one part to be treated, and a film mounted on the first side of the part holder opposite said through-hole, allowing said part to be treated to be held at least during the loading step.