Carbon brushes are cheap enough that most people don't think twice about them, and that is exactly where the false-economy trap lives. The cheapest brushes on the auction sites and from no-name suppliers tend to look right and fit right — but the graphite grade, the spring temper and the lead terminal are all places where corners get cut, and the cost shows up months later.
The graphite grade is the single biggest variable. A correct brush is a carefully blended graphite-copper mix tuned to the commutator material and the working RPM of the tool. Cheap brushes use cruder graphite that wears faster, runs hotter and — worst of all — abrades the commutator. A worn-out commutator is a motor rebuild, not a brush change. We see tools that have had three pairs of cheap brushes in a year and ended up with scored commutators that the next pair of brushes can't recover.
The brush spring is the second variable. A weak spring no longer pushes a worn brush firmly enough against the commutator, which causes the intermittent stop-start running that imitates a switch fault. Cheap brushes are often supplied without the spring, leaving the operator to reuse the original — fine if the spring is healthy, awkward if it isn't. The third variable is the lead terminal: a poor swage at the spade or screw end is the kind of failure you only notice when the tool stops running mid-cut.
The brands that do this work properly are the ones whose names you already know — Makita's own brushes, OEM-equivalent brushes specified to the same dimensions and graphite grade. We carry the direct-fit ranges under Makita, DeWalt, Bosch, Hitachi and HiKOKI, Hilti, Titan and Black & Decker.
The economics are simple. A brush that lasts twice as long and protects the commutator pays for itself the first time you avoid a motor rebuild. For a wider view across the rest of the wear parts, the tool parts hub sets out the same logic across brushes, bearings, belts and blades.