A plug for preventing corrosion of an attachment opening, includes a bottom surface including an opening for receiving a head of a tightening device; a top surface; and a substantially cylindrical side wall extending between the bottom surface and the top surface. The side wall includes a first side area, wherein the plug is formed of a elastically deformable material and has a diameter at rest and resiliency enabling the plug to block, and be held in, a top portion of the attachment opening via resilient change in shape; and the top surface includes at least one first blind hole, the shape of which is such that, when the plug is subjected to an elastic deformation that causes a ridge to appear between the top surface and the first side area of the plug, the ridge is removed by elastic deformation of the blind hole.