Metacaulk® Cover Guard? is a single component fire rated gasket for use with electrical boxes when addressing the "24 inch rule". Metacaulk® Cover Guard? is applied by hand, does not take up volume in the electrical box and is a labor saving replacement for putty pads in normal applications. STC rating 54*. Complies to Required Environmental Exposure Testing of Accelerated Aging and High Humidity as per UL 1479 Fire Test of Through-Penetration Firestops. U.S. Patent No. 6,207,085. *Tested in a UL 411 wall assembly/section to ASTM E90.