Omnipure K2553-BB Nitrate Removal Inline Water Filter The Omnipure K-Series K2553-BB inline filter features 1/4 FPT fittings on both ends. The Omnipure K2553-BB water filter reduces nitrates A520E. Dimensions: 2 W X 10 L. Contaminant Reduction: Nitrate Reduction A520E. Fitting Size: 1/4 FPT.