Installing reflective, colour-coded markers on your fire hydrants not only distinguishes them at night from other street level markers but indicates the gpm flow so crews can hook up appropriate hoses without wasting time checking files. Installed on the fire hydrant to help emergency personnel identify the location and flow rate of hydrants quickly in the dark. Out of Service. High Intensity Reflective. 7.5" Outer Diameter & 3.5" and 4.5" Inner Diameter options.