A nut is prevented from turning during screwing by a body attached to one of the parts to be tightened by rivets. The body prevents the nut from rotating via a ring coupled without clearance with the nut and coupled with radial clearance to the body, in order to allow the nut to self-position itself along the axis imposed on the screw by the bores traversed by the screw. The nut can thus be a standard nut or a floating cage nut. Application to the retaining of nuts that are inaccessible and/or require a high level of security against unintentional unscrewing.