This is all really interesting. By the way, my Really Old Dictionaries have a definition of "bush" that would fit Daniel's usage perfectly. It's also in my copy of Chambers.

1. A lining of harder material set into an orifice to guard against wearing by friction; the perforated box or tube of metal fitted into certain parts of machinery, as the pivot holes of a clock, the centre of a cart-wheel, &c.

(The Imperial Dictionary of the English Language, 1900)