20 Pcs Aquarium Accessories: 10 Pcs One Way Check Valve & 10 Pcs Aquarium Air Stone10 pcs gray mineral bubble air stone, help to refresh the dissolved oxygen in tank water and keep fish live in a better environment.Produce mini bubbles, increase the breeding density, effectively create water currents and improve water quality in tanks.100% Brand new and high quality one way check valve for aquarium air pump.Small and compactProtect you air pump by preventing aquarium water from back siphoning during a power outage and casing damage.Easy to install,Compatible with standard aquarium air pipe of 4mm inner diameterAquarium Air Stone:Product Name : Aquarium Air Stone;Stone Size : 24 x 15 mmConnector Size : 4 x 2.5mm Total Length : 38mmOne Way Check Valve:Overall Size:53x15mm (LxW)Material:plastic & Mineralcolour:Blue & Black + ClearPackage Contents:10 * One Way Check Valve10 * Aquarium Air StoneOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.