Orbit UFSI Universal Fireblok Firestop Insert For 1-gang, 4” & 4-11/16” Steel Box 30 PackOrbit UFSI UFSI Product Description FIREBLOK's Universal Firestop Insert is intumescent thermoplastic pad used as a membrane penetration fire stop in electrical boxes maintaining the fire resistant ratings of wall assemblies and when the horizontal separation between metallic boxes on opposite sides of the wall is less than 24 apart. The insert is certified for both 1 & 2 hour, U300, U400, V400 and U411 wall assemblies with metal electrical boxes with