The flow indicator provides immediate visual indication of water, air or gas flow. The white nylon ball rotates in a circular channel during flow. Continuity and relative flow rate are indicated by the speed of the ball's rotation. The minimum flow rate to acutuate the ball with water is 50ml/min. in horizontal position, 140ml/min. in vertical position. With air, the minimum flow rate is 3 liters/min. in horizontal position, 8 liters/min. in vertical position. Max-working pressure is 10 psi. There is an arrow for directional flow. Clear polystyrene. 39mm X 57mm with two 23mm tube extensions. Accepts 1/4" to 3/8" I.D. tubing.