The arm of a robot is usually referred to as a manipulator. This enables it to manipulate objects with its hand, which is called an end effector. Mechanical grippers are one of the most common effectors. It typically consists of two fingers which can open and close so that it can pick up or let go of a variety of small objects.
Manipulation Devices
Vacuum grippers are used by pick and place robots in factories for electronic components and for large objects as long as the surface would be smooth enough to enable suction. General purpose effectors are fully humanoid hands which are highly dexterous and have hundreds of tactile sensors.