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
Brass Flareless Tube Union
Tacoma Screw Products | 5/8" D.O.T. Air Brake Brass Fitting for Copper Tubing - Nut