Abstract: Example brush wear monitoring systems and assemblies of an electric machine are disclosed. An example brush assembly of an electric machine includes a carbon brush including an upper surface, a lower surface opposite the upper surface, and a longitudinal channel extending into the brush from the upper surface. The longitudinal channel includes a lower region having a first width and an upper region having a second width at the upper surface that is greater than the first width. The system may also include a spacer having a keel configured to be inserted into the longitudinal channel. The keel includes a base portion having tapering sidewalls extending downward from the body and a blade having first and second parallel sidewalls extending downward from the base portion.