A thrust bearing is a particular type of rotary bearing. Like other bearings, they rotate permanently between parts, but are designed to support a predominantly axial load.
Thrust bearings come in several varieties and are commonly used in automotive, marine and aerospace applications. They are also used in the grips of the main and tail rotor blades of RC (radio controlled) helicopters.
Thrust bearings are used in cars because modern automobile forward gear reducers use helical gears which, while aiding smoothness and noise reduction, cause axial forces that must be controlled.
Thrust bearings are also used with radio antenna masts to reduce the load on an antenna rotator. A classic release bearing in a car is the clutch release bearing.
There are also bearings that offer a combined axial/radial load, such as RAX combined bearings.
