A fastening system for attaching an NMR probe (1) to an NMR magnet (2) includes a discoid insert (3) and a retention system (4) that is rigidly connected to the magnet and on which the insert can be mounted. A form-fitting, variable-force connection is established between the NMR probe and the retention system using a spring element (8). The probe attaches to the insert by a plurality of integral,rigid retaining elements that are of an invariable fixed length. The spring element and the retaining elements (6) are designed geometrically such that in a first, opened state the connection betweenthe insert and the retaining elements has a mechanical backlash between 0.5 mm and 5 mm when the spring element is relaxed. In a second, closed state the connection between the insert and the retaining elements has no mechanical backlash when the spring element is under mechanical tension. Therefore, a certain retaining force is reached in the fastening final state and the mechanical gap is blocked.