Closing plug (10, 100) for closing an opening (20, 120), in particular in a body structure of an automobile, having: - an insert component (12, 112) adapted to be mounted in the opening, wherein the insert component comprises: a tubular body (22, 122) extending along a longitudinal axis between a first end portion and a second end portion and defining a hole (32, 132), the tubular body (22, 122) being provided with an inner surface facing the hole and an outer surface opposite the inner surface, wherein the inner surface comprises a pre-mounting element and/or a locking element,, a circumference collar (26, 126) extending radially outward from the periphery of the first end portion and adapted to rest against a first side of a body structure, - a lid component (14, 114) for cooperating with the insert component (12, 112) and adapted to be inserted into the hole of the insert component, wherein the lid component comprises a cylindrical general shape with a top side (70, 170) and a lateral side, wherein the lateral side has an outer locking contour and an outer pre-mounting contour, wherein the lid component (14, 114) is movable relative to the insert component (12, 112) along the longitudinal axis between a pre-mounted position, in which the pre-mounting contour cooperates with the pre-mounting element and the lateral side of the lid component is partly inserted into the hole, and a locked position, in which the locking contour cooperates with the locking element and the lateral side of the lid component (14, 114) is entirely inserted into the hole characterized in that the insert component further comprises a sealing element (24, 124) surrounding the outer surface of the tubular body and destined to be arranged in the opening, and in that in the locked position the lateral side of the lid component (14, 114) urges the sealing element radially outward. - an insert component (12, 112) adapted to be mounted in the opening, wherein the insert component comprises: a tubular body (22, 122) extending along a longitudinal axis between a first end portion and a second end portion and defining a hole (32, 132), the tubular body (22, 122) being provided with an inner surface facing the hole and an outer surface opposite the inner surface, wherein the inner surface comprises a pre-mounting element and/or a locking element,, a circumference collar (26, 126) extending radially outward from the periphery of the first end portion and adapted to rest against a first side of a body structure, a tubular body (22, 122) extending along a longitudinal axis between a first end portion and a second end portion and defining a hole (32, 132), the tubular body (22, 122) being provided with an inner surface facing the hole and an outer surface opposite the inner surface, wherein the inner surface comprises a pre-mounting element and/or a locking element,, a circumference collar (26, 126) extending radially outward from the periphery of the first end portion and adapted to rest against a first side of a body structure, - a lid component (14, 114) for cooperating with the insert component (12, 112) and adapted to be inserted into the hole of the insert component, wherein the lid component comprises a cylindrical general shape with a top side (70, 170) and a lateral side, wherein the lateral side has an outer locking contour and an outer pre-mounting contour, wherein the lid component (14, 114) is movable relative to the insert component (12, 112) along the longitudinal axis between a pre-mounted position, in which the pre-mounting contour cooperates with the pre-mounting element and the lateral side of the lid component is partly inserted into the hole, and a locked position, in which the locking contour cooperates with the locking element and the lateral side of the lid component (14, 114) is entirely inserted into the hole characterized in that the insert component further comprises a sealing element (24, 124) surrounding the outer surface of the tubular body and destined to be arranged in the opening, and in that in the locked position the lateral side of the lid component (14, 114) urges the sealing element radially outward. wherein the lid component (14, 114) is movable relative to the insert component (12, 112) along the longitudinal axis between a pre-mounted position, in which the pre-mounting contour cooperates with the pre-mounting element and the lateral side of the lid component is partly inserted into the hole, and a locked position, in which the locking contour cooperates with the locking element and the lateral side of the lid component (14, 114) is entirely inserted into the hole characterized in that the insert component further comprises a sealing element (24, 124) surrounding the outer surface of the tubular body and destined to be arranged in the opening, and in that in the locked position the lateral side of the lid component (14, 114) urges the sealing element radially outward.