The Stern Defense 9mm Bolt Replacement Kit is a great choice if you need to rebuild the bolt out of your old workhorse after thousandfs of rounds. It is also handy to keep around in case a part unexpectedly breaks, or gets lost. IncludesCustom 4140 billet extractor providing superior ejection.Extractor pin.Extractor spring.Firing pin.Firing pin Spring.Firing pin retaining pin. Note: Designed to be used with the SD BU9 only.