This is required whenever the installed firestop sleeve system is to be left empty of cables, even overnight or on weekends. UNIQUE threaded Endcaps seal the ends of our empty threaded Firestop Sleeve Systems in new installations or in abandoned sleeves. Threaded Endcaps for Empty 1 Inch Diameter Threaded Firestop Sleeve This firestopping putty should be used to seal the sleeve either permanently or until the new cables are installed and may be used again when the sleeve is put back into service. UL Classified for up to 4 hours.