PETT112 Poly Insert Tee, 1-1/2 Inch. A tee is a plumbing fitting that allows you to connect three sections of polyethylene tubing. Each of the three connections has barbed connections measuring at 1-1/2 inch nominal size. This fitting is specifically for use with 1-1/2 inch 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.