if you refer to the pic in the link that paul provided, the bosch brushes have a little nub at the end
if you can find an automotive brush with a little nub, it will be better than one without because the spring can hold onto the brush better because of it. my local surplus store has ones with brushes and springs held together with little retainers, ie, solder the retainer, assembly fixed. remember, no matter what kind of brushes you get, they must be similar in size to the ones you are replacing when you get finished (ie, you can shave down a oversized one, but in an alternator, there's no room to make two smaller ones into one larger one).