This is needed if you have activated your PFD, or if those parts have not passed your yearly PFD self inspection. These parts allow you to perform PFD self inspections and replace these parts as needed. It includes a cap that can temporarily disable the Auto water-sensing inflation feature of your PFD if you want to.
This is for Adult PFDs only. For Auto/Manual Childrens PFDs, there is another version with a 17 gram cylinder.