Device for extruding hollow strands from thermoplastic material, with an extruder head, having a mandrel, and a calibrating device, for making a dimensional change while production is in progress, and with a radially adjustable inlet, at least one Ranque vortex chamber being formed in the mandrel, the cooling air outlet of which chamber leads into a cooling tube, which extends as an axial extension of the mandrel through the inlet of the calibrating device and has a cooling air outlet opening out into the calibrating device. This device achieves the object of providing a device with which effective interior cooling is achieved in calibrating devices designed for making a dimensional change while operation is in progress.