Sprinklers, Dry : A sprinkler secured in an extension nipple that has a seal at the inlet end to prevent water from entering the nipple until the sprinkler operates
NFPA 25 Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 2008 ed. https://law.resource.org/pub/us/cfr/ibr/004/nfpa.2 5.2002.pdf, (Std: Insp, Testing, and Maint of Wtr-Based Fr Prac Sys - Amer) {191 NFC}