The K2548 inline calcite filter is one of Omnipure's K series inline filters that easily install directly to your water line and reduce weeping or seepage potential. This filter contains calcite, a crushed and screened white marble media, to neutralize acidic or low pH waters to a safer, less corrosive effluent. Available with various fittings to meet your water line's specifications. NOTE: 1/4" and 3/8" refers to the outside diameter of tubing. Specifications: Dimensions: 10" X 2" Replace every 6-12 months Corrects acidic/low pH water Available Fittings: BB = 1/4" FPT CC = 3/8" FPT JJ = 1/4" Quick Connect KK = 3/8" Quick Connect 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.