Abstract: This invention describes a retaining device for holding, guiding and self-actuated releasing of assembly and auxiliary assembly parts, such as nuts, bolts, and rivets, in a device for pressing or attaching the parts to sheet metal, illustrated here with nuts as an example. The retaining device is used to hold the nuts in a definite, stable position during their transport from a starting position to the working position. It consists of two retaining catches that are pivotably mounted to the plunger so that they can be pivoted between a closed position in which they hold the nuts against the plunger, and an open position in which they release the nuts. A restricted guidance element for the retaining catches ensures that during an outward thrust movement of the plunger, the retaining catches remain in their closed position and will only be released to pivot into the open position after the plunger has reached the working position.