These rubber light bar silencers plug into the fins on the back of our Street Series LED Light bars to reduce the wind noise common with rooftop aftermarket installations • Use (1) Noise Reducer every 12″ for best results -Use (1) for 10″ Light Bars -Use (2) for 20″ Light Bars -Use (3) for 30″ Light Bars -Use (4) for 40″ Light Bars -use (5) for 50″ Light Bars