Safety Technology International, Inc. STI-9602 Steel Web Stopper, 9 Gauge Corrosion Resistant Polyester Coated Cage, Surface Mount, 4.25" Depth UL listed cage for areas where abuse to smoke detectors is severe Constructed from heavy gauge steel wire with corrosion resistant polyester coating Cover is for surface mounted smoke detectors Simple removal for servicing the detector Dimensions  8.25 diameter x 4.25H