The Hydro Flow? Poly Dripper Lines are used as feed lines from the distribution poly tubing line. These dripper lines are used to connect Hydro Flow? Blue or Black Dripper Stakes (#747196, 742415, 747198 or 742420). The Hydro Flow? Poly Dripper Lines may be installed above or below ground. The line has an inside dimension of 3/16 inch and the outside dimension is 1/4 inch at 15 inch of length.