Manipulator arm

The manipulator arm, tactile arm (PROSE: Davros Genesis) or arm-stick, (PROSE: Death to the Daleks) was a long, thin, mechanical arm found on all Dalek models except for the Emperors, the Time War Emperor's guards and special weapons models. The manipulator arm was found in the right-hand socket in the Dalek weapons platform, with the gunstick on its left. Its function varied depending on its design, and it could be swapped out for a tool more specific to the Dalek's current needs.

Development
Following Davros' early prototype, Dalek One sported a tactile arm. (PROSE: Davros Genesis)

Plunger
The ends of the manipulator arms typically were shaped like a plunger, known as suction arms. (PROSE: Prisoner of the Daleks) For this reason, Dalek technology often had circular controls which the Daleks could arm or disarm by rotating. The black tip at the end, which gave the arm its "plunger" shape, could alter its form to better interact with specific objects, for example, finding the combination of electronically-locked doors. (TV: Dalek)

Even if the Dalek died, its arm could still operate machinery for a live person (TV: Remembrance of the Daleks). The arm also had a telescopic feature to extend its length. (TV: The Dalek Invasion of Earth, Dalek)

It could also serve as a weapon; with the tip placed over the nose and mouth, the arm could generate suction to suffocate and kill a human and enough traction to crush a human skull or rip through sheet metal. (TV: Dalek, TV: Doomsday, PROSE: I Am a Dalek) The Tenth Doctor claimed to have seen one crush a brick with ease. (PROSE: Prisoners of the Daleks)

At least in the case of the Cult of Skaro, the arm could also scan brainwaves for information or act as a quick intelligence scan. (TV: Doomsday, Daleks in Manhattan) However, if a large amount of information needed to be analysed, it could be drained out by force by encasing a subject's head inside their "plunger" tips, which would stretch the victim's head and brain to wring out their knowledge through information probes. The probes were strong enough to have a deadly effect on humans, draining them so fiercely that their bodies shrivelled up and became burned out husks. (TV: Doomsday)

Imperial Daleks had a more conical variant, with a slotted rim specifically designed to operate controls. (TV: Remembrance of the Daleks)

In an alternate timeline, the Scientist Dalek of the Dalek Time Squad possessed a manipulator arm that closely resembled the traditional plunger seen on most Daleks, but with six claws attached to the end. (PROSE: The Guide to the Dark Times)

Flamethrower
Referred to by Daleks as pyro-flames, these were small cylindrical pieces at the end of the arm which shot a stream of fire to clear swaths of forest. (TV: The Daleks' Master Plan) The Daleks later used other flamethrowers, which they referred to as flame guns, to melt through ice when searching for "the Abomination". The ends resembled the Progenitor Daleks' eyestalks. (COMIC: The Only Good Dalek) Daleks in the First World War used flamethrowers to clear forests to pursue the Eleventh Doctor and his companions. The flames came from their arms. (COMIC: The Dalek Project)

Seismic detector
A small device which looked like a compass suspended on gimbals, the seismic detector was employed to locate enemy time machines outside the vortex. It could also detect approaching life-forms or the paths of fleeing ones, even through sealed doors. (TV: The Chase)

Electrode unit
The electrode unit was a device which looked like a radar dish. It could operate electronic controls remotely. It was used in this manner to enter the Mechanoid City. (TV: The Chase)

Sieve
Dalek mutants were inserted into the Dalek shell during assembly by a Dalek fitted with a sieve instead of a plunger. (TV: The Power of the Daleks)

Syringe
Dalek Jast of the Cult of Skaro had an alternative attachment - a syringe. The syringe was fastened directly to the end of the manipulator arm in place of the plunger. (TV: Daleks in Manhattan)

Blowtorch
To cut through doors, early Daleks used a long, thin instrument with two spheres and a clear disc set midway up. (TV: "The Ambush") Assault Daleks had a claw and blowtorch combination. These were used for cutting through strong metals such as Hydra Combination and for picking up objects normal Daleks couldn't. (TV: The Parting of the Ways, PROSE: Prisoner of the Daleks)

Cutting tool
The Daleks used a hot iron to cut through metal. On Spiridon they used one to cut through a thick door. (TV: Planet of the Daleks)

Alternative weapons
Two alternative weapon was seen on two of the Emperor's Personal Guard. One seemed to be an upgraded Dalek gunstick, but significanty larger, and with a large sphere on the end. The other side still possessed a gun. (TV: The Parting of the Ways)

Another of the Dalek Emperor's guards had an arm with forward-jutting silver protrusions on a small ball. (TV: The Parting of the Ways)

Dalek X's elite guards had no manipulator arms, but instead had double gunsticks. (PROSE: Prisoner of the Daleks)

In an alternate timeline, the Dalek Executioner of the Dalek Time Squad possessed a manipulator arm with a claw with three crescent-shaped blades, in place of the traditional plunger. (PROSE: The Guide to the Dark Times)

Other variants
On Earth in 2019, a reconnaissance scout Dalek built itself a new casing to replace the one destroyed by humans in the 9th century. This new casing, constructed from a combination of Earth metals and remnants of the Dalek's original casing, featured a claw-like manipulator arm instead of the traditional plunger arm. (TV: Resolution)

During the Last Great Time War, the Black Dalek overseer had a unique manipulator arm as well as several other appendages attached to its weapons platform. (AUDIO: Planet of the Ogrons)

Daleks in the Vault in the Crucible had a diamond-shaped interface to work with machinery and technology within the Vault. They resembled eight clawed arms. (TV: Journey's End)

A Dalek on the Dalek Saucer Survey Ship Sigma used a fire extinguisher arm to put out the fire after the ship collided with Survey Ship Delta. (COMIC: The Dalek Project)

The "Quasimodo Dalek", which was reconstructed by unfamiliar humans, had an eyepiece fitted in place of its manipulator arm as well as its gunstick, which was fitted in place of the eyepiece atop the dome. (COMIC: The Dalek Project)

The robotic Proto-Daleks, which were constructed by the British and Germans as part of the Dalek Project during the First World War, sported manipulator arms similar to those used by true Daleks, but mounted on a pivot rather than a balljoint. (COMIC: The Dalek Project)

Behind the scenes

 * A manipulator arm, specifically the suction arm, was notably the very first part of a Dalek to appear on-screen, as seen attached to the Dalek which confronts Barbara Wright within the Dalek City at the very end of their first episode, "The Dead Planet". The Daleks would only be revealed in full in their second episode, "The Survivors".
 * In the two Dalek films, Dr. Who and the Daleks and Daleks' Invasion Earth 2150 A.D., the Daleks alternately appear with suction cups or a two-fingered claw manipulator, which was not derived from the original serials; the films' basic Daleks, Blue Daleks and Silver Daleks respectively, appear alternately with suckers or claws, higher-ranking individuals such as the Red Dalek of Dr. Who and the Daleks, the Red Dalek and the Black Dalek of Daleks' Invasion Earth 2150 A.D., sport claws, while the Black Dalek of Dr. Who and the Daleks and the Gold Dalek of Daleks' Invasion Earth 2150 A.D., whom functioned as the Supreme Dalek leader in their respective films, sported sucker arms.
 * In the online video game, The Last Dalek, the player can use the "Metaltron's" extending suction arm as a close-quarter weapon. The suction cup's ability to bypass locks is utilised via a Bio Processor.
 * One Battles in Time trading card features a Dalek with a buzz-saw attachment. This is only seen in the Doctor Who book Prisoner of the Daleks, where a Dalek tries to use the buzz-saw to remove Space Major Jon Bowman's brain. In some magazines these Daleks are shown to have a black skirt.
 * A rare Black Dalek figure has a buzzsaw arm, reflecting CGI models made for The Parting of the Ways, but screen resolution makes it unclear if it was actually used on-screen.
 * Another used a "claw probe".