A carbon brush, also known as a motor brush, is a very small part of an electric motor that conducts the electrical current between stationary and rotating wires inside the motor/generator.
A carbon brush is typically made of one or multiple carbon blocks, with one or more terminals. Carbon is used as it's a reasonably good conductor of electricity, while it is soft enough to give a consistent contact point. However this soft property means it does wear over time, and hence the need to regularly replace carbon brushes.
You will typically find more than one carbon brush in each motor, and there are different types for different types of motors/tools.
Carbon brushes work by reducing the damage to the motor, by carrying the current back and forth between the stationary and moving parts of the motor. Instead of having an integral part of the machine wear away from this process, these are easily replaceable parts that are designed to wear away.
If your power tool isn't working, then check out our range of replacement carbon brushes for power tools here.
Learn more about how to know when to replace a carbon brush here.