These are usually ball bearings, although some headsets use needle bearings.
head | head of state | Beavis and Butt-head | Alec Head | Murray Head | Head Start | Anthony Head | Head Start Program | Diamond Head | The Tube | Human head | Head teacher | Machine Head (band) | Machine Head | Head Over Heels | Head of the River Race | Eddie the Head | Cathode ray tube | Hilton Head Island, South Carolina | Edith Head | Diamond Head (band) | Beachy Head | X-ray tube | The Tube (TV series) | The Groove Tube | The Bodley Head | Lizard Head | Head & Shoulders | Head over Heels (Paula Abdul album) | Head over Heels |