Device and method and assembly for inserting auxiliary joint into workpiece

The invention relates to a device (10) for inserting an auxiliary joining part (22) into a workpiece (8), the auxiliary joining part having a circular circumference in a section to be pressed into the workpiece, the circumference having a maximum first diameter, having a die (14) for resting on an underside of the workpiece during the pressing of the auxiliary joining part, wherein the mould has a contact region (24) and a recess (26) surrounded by the contact region, an edge (28) of the recess deviates from the circular shape, a section of the edge of the recess, which section is located farthest outward in the radial direction, lies on an imaginary circumcircle (34), and wherein a section of the edge of the recess, which section is located farthest inward in the radial direction, lies on an imaginary incircle (36), wherein the edge of the recess has at least three projections projecting into a circumcircle of the recess, and wherein the projections touch an inscribed circle wherein the diameter of the inscr