Although co-extrusion uses two extruders, the materials produced in them run through the same die. The co-rotating twin screw extruder compounds the active ingredient and the polymer. A second extruder (often a single screw extruder) shapes the outer layer, which consists of pure polymer. The outer membrane controls the drug release and has a dissolution rate of almost zero order. Since a uniform diameter must be ensured here, a melt pump is often placed between the extruder and the co-extrusion die. After the cooling down (in the water bath), a pulling device produces the tension of the extruded product. Then the cut is made. Ultimately, the pulling device gives the magnitude of the diameter. When necessary, it is adjusted by means of a laser micrometer. The laser micrometer measures the outer diameter of the extrudate and sends the information to the pulling device, which adjusts itself accordingly. The best-known co-extruded implant is the hormone-containing Nuvaring® or Implanon®.