Zenith variac type 100r - carbon brushes

[ppppenguin]

According to this article (and many others), graphite is naturally anisotropic: https://asbury.com/resources/education/g...nisotropy/ If you think of the layer structure in graphite, this is hardly surprising.

The makers of carbon brushes probably use quite a lot of knowhow to get the right combination of electrical and mechanical properties for different applications.