Works with 3" round reflectors Plastic Construction PhotoCell Replacement Protective Hood with 3" Reflector Retroreflective High Impact 3" Round Reflector and Protective Hood ( Only ) Reflector, Retro-reflective, Length 3.00 In, Width 3.00 In, Depth 0.35 In, Mounting Hole Center, For Use With Photoelectric Sensors Corner Cube Reflectors Retro-reflector prisms return a beam in the same direction it came from even if the reflector and the source are skewed for a high degree of reliability.