Assembly including a body of a motor vehicle and including a finishing part, the body having a first trim and/or protective body portion and a second trim and/or protective body portion, the finishing part being designed to link the first body portion and the second body portion, * the first body portion ending in a sheet edge, * the second body portion having a substantially flat portion facing the sheet edge and being traversed by an orifice, * the finishing part having: - a first end and a second end, - a docking face, - a first portion including the first end, - a second portion including the docking face and extending as far as the second end, - engagement reliefs (11, 12, 13, 14) integral with the part, including at least a first relief projecting from the first portion, a second relief projecting from the docking face and at least one third relief (13, 14), the first, second and third reliefs being designed to engage the part with the edge of the first body portion using the first engagement relief and to press the docking face flat against the second body portion by inserting the second relief through said orifice in the second body portion such that, once in the assembled position, the part is engaged with the edge of the first body portion by the first engagement relief and the docking face bears flat against the second body portion, since the finishing part is designed to be assembled on the body essentially by direct cooperation of each engagement relief (11, 12, 13, 14) with at least one edge or an orifice (22, 23, 24) in the body, characterized in that the first relief, the second relief and the third relief are designed to be placed, when the finishing part is assembled on the body, on the edges or in the orifices (22, 23, 24) in the body that match said reliefs, respectively in a first insertion direction, a second insertion direction and a third insertion direction that are perpendicular to one another in pairs, the first direction being parallel to a longitudinal direction linking the first end and the second end, the first relief being a hook-shaped tab extending substantially parallel to the longitudinal direction from a base linked to the first portion of the part, the first engagement relief forms a tab extending lengthwise in the longitudinal direction from the base of the tab attached to the first portion such that the base of the tab is longer than it is wide, such as to facilitate, during assembly of the finishing part, a rotational movement in a plane substantially parallel to the mid plane of the docking face about a centre of rotation in the first portion of the finishing part, engaged with the edge of the first body portion by the first engagement relief, the second relief being a second hook-shaped tab designed to be inserted behind one edge of the orifice, and the third relief being at least one retaining lug substantially perpendicular to the docking face, the third relief having a non-return end designed to provide a harpoon lock. * the first body portion ending in a sheet edge, * the second body portion having a substantially flat portion facing the sheet edge and being traversed by an orifice, * the finishing part having: - a first end and a second end, - a docking face, - a first portion including the first end, - a second portion including the docking face and extending as far as the second end, - engagement reliefs (11, 12, 13, 14) integral with the part, including at least a first relief projecting from the first portion, a second relief projecting from the docking face and at least one third relief (13, 14), the first, second and third reliefs being designed to engage the part with the edge of the first body portion using the first engagement relief and to press the docking face flat against the second body portion by inserting the second relief through said orifice in the second body portion such that, once in the assembled position, the part is engaged with the edge of the first body portion by the first engagement relief and the docking face bears flat against the second body portion, - a first end and a second end, - a docking face, - a first portion including the first end, - a second portion including the docking face and extending as far as the second end, - engagement reliefs (11, 12, 13, 14) integral with the part, including at least a first relief projecting from the first portion, a second relief projecting from the docking face and at least one third relief (13, 14), the first, second and third reliefs being designed to engage the part with the edge of the first body portion using the first engagement relief and to press the docking face flat against the second body portion by inserting the second relief through said orifice in the second body portion such that, once in the assembled position, the part is engaged with the edge of the first body portion by the first engagement relief and the docking face bears flat against the second body portion,