Docking clamp
From Tardis Wiki, the free Doctor Who reference
A docking clamp connected the dome of a Dalek to their upper grating section. By releasing their docking clamp, a Dalek could open up their dome, exposing their mutant form. (TV: Resurrection of the Daleks)
While operating a vacant Dalek casing within the Moroks' Space Museum, the First Doctor opened up the dome to peek his head out of the casing. (TV: The Space Museum)
Aboard a Prison Station, two Daleks sent by the Supreme Dalek released their docking clamps, ostensibly so that Kiston could extract samples of Dalek tissue for Davros' research into the Movellan virus. In reality, the device used by Kiston, once administered to the mutant Daleks, conditioned them to obey Davros. (TV: Resurrection of the Daleks)
