Bendable Bubble wall 60cm 23.6" - Air Stone curtain tube pump for 4/6mm tubing Permeable Flexible Air Stones are a great way to aerate your growing system. The flexible stones bend into any shape you need to deliver air where you need it most, they also create less back pressure than traditional air stones, which reduces damage to your pump. Measures approximately: SIZE 60cm (23.6") and 0.85mm in diameter.. for 4/6mm air tube.