PETL34 Poly Insert Elbow, 3/4 Inch. An elbow is designed in order to connect two sections of piping together. The fitting has a 90 degree right angle design in order to create a sharp turn in the pipe when needed. It features 3/4 inch barbed connections on either side and is specifically used in order to connect two sections of polyethylene tubing. Poly fittings are used in multiple water applications but should never be used in gas, steam or compressed air applications. The fittings are specifically designed to work with polyethylene tubing (aka Poly Pipe, Poly Tube). In order to create a secure and tight connection, hose clamps should be used. The barbed connections of the poly fittings work well to hold tight to the pipe, but water pressure can push the tube off the fitting, making the hose clamps a great choice for installation.