The Omnipure K-Series K5655-BB inline filter features 1/4" FPT fittings and 1/4" QC fittings on both ends. This filter features an ion exchange process producing deionized water which is water that lacks ions, such as those from sodium, calcium, iron, and copper. Dimensions: 2.5" W X 12" L Filtration Media: DI Mixed Bed Resin Fitting Size: 1/4" FPT and 1/4" QC National Pipe Thread (NPT) Size Measured Against a Ruler* Actual Diameter (Inches) National Pipe Thread (NPT) (Fractional) 0.405" 1/8" 0.540" 1/4" 0.675" 3/8" 0.840" 1/2" *NOTE: A very common misconception is that a 1/4" NPT measures as 1/4 inch on a ruler or tape measurer. However, that is not the case. NPT will measure larger in diameter. Above is a sizing reference to help clarify.