This is the electric window lift motor gear (Worm Gear).  1979-1980 Silver Shadow II, Silver Wraith II, Bentley T (VIN 36422 onwards) 1981 Sliver Spirit, Silver Spur, Mulsanne, Eight, Turbo...

Window Motor plastic coupling that goes between the pin on the window motor and the worm shaft gear inside the gearbox. From 1978 VIN 36500 approx until 1987  

This is the plastic coupling between the window lift motor and the gear box.  1981-1998 From VIN 1001 onwards