This is the Buckeye Workman cartridge with a pore size of 5 micron nominal.  The recommendation by RO membrane manufacturers for use of a carbon block of 5 micron or smaller to protect the membrane makes these blocks the most widely used.  Made from coconut shell carbon, with a polypropylene wrap, end caps, and protective netting with neoprene gaskets.  Chlorine capacity varies by the size of the carbon block:

• 5" x 2.5"     3,000 gallons @ 0.4 gpm
• 10" x 2.5"   6,000 gallons @ 0.75 gpm
• 20" x 2.5"   9,000 gallons @ 2.0 gpm
• 10" x 4.5"   12,000 gallons @ 3.5 gpm
• 20" x 4.5"   26,000 gallons @ 7.0 gpm

Higher chlorine capacities will be realized with slower flow.  For reference, flow through a 75 gpd RO system with a 4:1 waste water to purified water ratio (20% recovery) is approximately 0.3 gpm. 

10" x 2.5" alternate part no. H00115.