Abstract: A tool for curling of can necks as part of a tool plate that includes an expansion control device for controlling of the spreading of a collet, a collet clutch, an interconnecting means provided with a stop mechanism, and a holder being fixed in the collet clutch at its one end, the collet being arranged on its other end, the collet in the non-active position being insertable into the can to permit segments of the collet to spread in the direction of the device.