Features: Plastic aquarium valves Made of durable clear plastic, small and compact, excellent water resistance Air hole diameter is 3mm , compatible with standard aquarium air hose about 4mm inner diameter , is easy to assemble. Functions: The valves are suitable for aquarium or fish tank, a measure protection device to protect your air pump by preventing the aquarium water from being sucked in when the power fails. Specifications: Material: Plastic Color: Black, Clear Vent Hole Diameter: 3mm/0.12inch Overall Size: 42mm x 13mm /1.65inch x 0.51inch (Length x Max Diameter) Promotional packaging: 12 * clear plastic valves