Blind rivet nuts and manual riveting tongs or pliers for setting them are already known. The blind rivet nut consists of a hollow rivet with an internal thread (inner screwhead) which has a setting head or setting flange (rivet nut head). The internal thread does not extend over the entire length of the hollow rivet but, corresponding to the size of the hollow rivet or to the thickness of the material to be worked, commences at a certain amount below the head. The manual riveting tool has a threaded mandrel which extends by an adjustable amount out of the housing and onto which the blind rivet nut is screwed. After the rivet nut has been inserted into the hole intended for the riveting the pull mechanism which bears the threaded mandrel is withdrawn into the housing by manipulating the arms and an annular bead is formed on the rivet nut as counterpart to the manufactured head on the other side of the workpiece which is to be worked. The threaded mandrel is then screwed out of the blind rivet nut which has been set. In this way one can produce a rivet connection between two or more workpieces, onto which a further part can, by means of the internal thread of the blind rivet nut, also be detachably fastened by a screw. In addition the blind rivet nut can also be set in a single workpiece, for instance a plate, in order to create the prerequisites for the threaded attachment of another part to this workpiece. The threaded mandrel is available of course in different thread sizes corresponding to the blind-rivet nuts, for instance in the DIN range of M3 to M6; it must thus be replaceable.
One great disadvantage of the known manual riveting tools for the setting of blind-rivet nuts is that they have an invariable actuating stroke, which is the longest required. Since a smaller thickness of workpiece material requires a larger stroke and a larger thickness of material requires a smaller stroke, the operator had to proceed intuitively when using the known manual riveting. The two tong arms had to be squeezed together until the annular bead was formed on the rivet nut on the opposite side of the workpiece, which side is generally not visible; relative displacement of the arms then was required to stop since otherwise the pull mandrel would tear off the thread of the nut. Since the operator had to proceed in accordance with a sense of feel in order to determine the time when the annular bead was formed, rapid work was impossible and defective rivetings constantly resulted due either to the fact that the blind rivet nut was not actually seated firmly because one proceeded too cautiously or to the fact that the thread of the rivet nut was damaged. In order that the thread of the rivet nut be uniformly acted upon during the riveting, the threaded mandrel should always extend out of the housing to such an extent that all threads of the blind rivet nut can be acted on. Corresponding to the different lengths of the rivet nuts the threaded mandrel extending out of the housing of the tongs can therefore be adjusted and fixed in length. For this purpose, a tool, for instance a wrench, is necessary with the known manual riveting tongs, which constitutes a disadvantage. The operation of the known manual riveting tongs is furthermore made difficult by the fact that the replacement of the threaded mandrels is also very complicated and is possible only with the use of special tools.