You are purchasing 5 x high quality 50mm (2inch) air stones suitable for aquarium and pond use.     <br /><br />These air stones will connect to standard 4/6mm air line. Or， the hose tail can be cut to accommodate thicker air line.<br /><br />5 x 50mm 2" Round Air Stones for Pond or Aquarium Fish Tank<br /><img src="http://img6.eachbuyer.com/x9/p100/tgt00688_1.jpg" />