Hydronix CB-45-2005 NSF Carbon Block Filter 4.5" OD X 20" Length, 5 Micron Carbon block filter for a water filtration system 4.5" OD and an overall length of 20" Coconut shell carbon filter media with polypropylene outer/inner wrap, end caps and netting Particle retention size of 5 micron Meets ANSI/NSF Standard 42 certification for material requirements only