Safety Technology International, Inc. STI-9610 Steel Web Stopper, 9 Gauge Corrosion Resistant Polyester Coated Cage, with High Profile, Surface Mount, 6" 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 high profile surface mount Simple removal for servicing the detector Dimensions  8.25 diameter x 6H