A fastening mechanism is provided to detachably fasten and position a compaction module on a drafting unit of a spinning machine, wherein the compaction module has a carrier, which is provided with at least one suction channel that is connected to suction inserts of compaction elements that are movably mounted on the carrier. A coupling device using the fastening mechanism. In order to ensure simple and positionally accurate attachment of a compaction module, the fastening mechanism is composed of at least one clamping element that has retaining elements for fixed and positioned fastening on the spinning machine and is provided with a first receiving slot, which is open on one side and has a retaining section, by means of which a retaining element fastened on the carrier can form a positive-fitting clamped connection.