S&S offers their steel breather kit as an upgrade to your standard breather gear. Consider this gear especially if you have a factory nylon gear in your engine - the nylon can readily accept shavings and carbon particles, turning itself into a giant abrasive wheel. Thoughtfully, S&S also offers this part in an .030" oversize version for those who have scored cases from their nylon breathers. If that's the predicament you find yourself in, you can have your machinist open up the breather bore, install the steel breather gear, and put your engine cases back into service!