These NSF Approved Alpine Pure System Housings are for those of you that want the best water flow and maximum dirt/chlorine/heavy metals holding capacity available. Manufactured with 1" BSP ports. Package includes 2 X 20" BIG Blue housings, Twin Stainless Steel bracket with SS screws, spanner and a 25mm housing joiner. Suitable for all our 20" X 4 1/4" filter cartridges. In a rural situation for sediment control we recommend the 50-20 micron Gradient Density followed by a 20-1 micron final cartridge. If Taste or Odor is an issue then the 20-1 micron Gradient Density goes first followed by a Carbon Block 5 or 10 micron depending on your budget. For Chlorinated town water a 20-1 micron Gradient Density always goes first followed by the 0.5 micron carbon block PB1 for the Ultimate protection or the 5 micron CTO for Chlorine, Taste and Odor removal.