UNIQUE threaded Endcaps seal the ends of our empty threaded Firestop Sleeve Systems in new installations or in abandoned sleeves. Sets of 2. UL Classified for up to 4 hours.Firestop sleeve systems are not allowed by ANY jurisdiction to be left open and unattended EVER, not even overnight. UNIQUE Smooth Endcaps are designed to seal the ends of our empty Threaded Firestop Sleeve Systems in new installations or abandoned/empty sleeves. This is required whenever the installed firestop sleeve system is to be left empty of cables, even overnight or on weekends.The required intumescent putty is included with the Endcap Systems. 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.