These in-line sanitary filters are manufactured specifically for filtering air, unlike other filters which are designed for water filtration and sold as though they will filter air just as efficiently. The HEPA filter utilizes a hydrophobic PTFE membrane in an acrylic housing. The clear acrylic housing allows instant visual inspection for contaminates, and the large square filter has greater surface area than other filters. The hose connections are 1/4" barbed.