Proline Series 1/2-in x 1/2-in Compression Coupling Union Fitting in the Brass Fittings department at Lowes.com
Amazon.com: 4 Pcs 3/8'' OD Compression Union Brass Compression Tube Fitting 3/8'' OD Compression Tube Connector Use with Copper, Aluminum, Plastic Tubing, Watertight Seal Waterlines or Air Pneumatic : Industrial & Scientific