The upgraded firing pin safety system consists of: the firing pin, firing pin safety, the extractor, the spring loaded bearing and the trigger bar. The upgraded system is applicable only to Glock pistols with the following serial number ranges :
Glock 17 - alpha prefixes AA - WF
Glock 19 - alpha prefixes through WJ
Glock 20 - alpha prefixes through WW
Glock 21 - alpha prefixes through XL
Glock 22 - alpha prefixes through YA
Glock 23 - alpha prefixes through SK