316 Stainless Steel, 3/8 in x 1/4 in Fitting Pipe Size, Hex Coupling - 1DGB9|6-4 FHC-SS - Grainger
Amazon.com: 2 Pack - 316 Stainless Steel 1/4 NPT Male to 1/4 NPT Male Straight Hex Coupler/Coupling for Air, Liquid or Hydraulic Fitting - Industrial Air Tool Hose 1/4 Inch Coupling : Industrial & Scientific