This is an authentic Ryobi replacement part that has been sourced from the original manufacturer to be used with belt sanders. The carbon brush is used to carry electricity to the armature by pressing against the commutator bars. The brush eventually wears out because of friction created by the rotation of the armature and the pressure fr...Read moreom the spring. This part assembly includes the carbon brush, the holder, and the spring. The assembly is sold individually, please note two may be needed.