LTWFITTING 1/2 in. O.D. Brass Compression Coupling Fitting (20-Pack) HF62820 - The Home Depot
1/4" MNPT 1/2" OD Push to Connect Tube Fitting — Milton® Industries Inc.
Uxcell Compression Tube Fitting 1/2" Tube OD Bulkhead Union 304 Stainless Steel - Walmart.com
Amazon.com: Push to Connect Air Fittings 1/2,CEKER PC 1/2 Inch Od Tube x 1/2" NPT Male Thread air line Quick Connect air Hose Fittings Pneumatic Fitting Push Lock Fit Connector 2Pack :