Hydronix sdp-4520 sediment dual purpose radial flow carbon filter is compatible with rfc-20bb filters. It provides a unique design combining all the benefits of a granular activated carbon (GAC) filter and that of a sediment filter. This filter produces higher flow rates and lower pressure drop while providing you with exceptional chlorine taste and odor reduction. The sdp-4520 cartridges have a radial flow design and are ideal for higher flow point of entry (PoE) applications. Specs: part sdp-4520 - rating: 25 microns - dimensions: 4 1/2" x 20" - flow rate: 0.9 psi at 4 gpm - fits most 20"x4.5” filter housings.