An assembly unit includes an assembly part penetrated by a through opening and a cylindrical sleeve which is captively fixed in the through opening. The sleeve has at least one spring element which protrudes from an external face of the sleeve by an excess length in a non-assembled state. The excess length is dimensioned such that the spring element is elastically moved radially inward by contact with the wall of the through opening when the sleeve is introduced into the through opening, so that the spring element presses against the wall 4 of the through opening as a result of elastic restoring forces.