Safety Technology International, Inc. STI-9601 Steel Web Stopper, 9 Gauge Corrosion Resistant Polyester Coated Cage, Flush Mount, 2.75" Depth UL listed cage for areas where abuse to smoke detectors is severe Constructed of 9-gauge Steel wire with corrosion resistant polyester coating Cover is for flush mounted smoke detectors Simple removal for servicing the detector Dimensions  8.25 diameter x 2.75H