Could you be more specific as to the application?
The Height depends on expected wear on the brushes as to width and thickness this will give you the area which will determine Current per square in (or cm2)
Whatever you use make sure the brushes are properly seated,
Or as close as possible to 100% of the brush area making contact.
I would guess that the best way would be to look at the "pigtail" wires on the brush and then size them so that the brush wires are 1.5 to 2 times the area of the wire leading to (or form) the brushes, but that is only my best guess.
Good Luck, Dan76