Big Blue 20" Dual Gradient 1 Micron Polypropylene Sediment Water Filter. 20" long X 4 1/2" diameter. 6 per case, sold individually. Ametek # 155360 DGD Series is manufactured from 100% pure polypropylene fibers and are sized for use in our Big Blue® filter housings. They are designed for purity and will not impart taste, odor or color to the liquid being filtered. Also, the polypropylene construction provides superior chemical resistance and is not prone to bacterial attack. The DGD Series advanced design combines selective "final filtration" with appropriate "pre-filtration." The larger diameter of the prefilter, pre-filter, pre filter reduces the particle load to the post filter, allowing it to operate at higher velocities. This increased depth provides for very high particulate reduction efficiencies and loading capacities. Order a case and save even more.