Sioux Chief® 5/16" ID Barb x 3/8" MIP Brass Adapter at Menards®
2 Brass SAE Brake Line Adapter 3/16 Female 3/8-24 X 5/16 (1/2-20) Male Inverted | eBay
5/16" Flare x 3/8" Male Brass Adapter - Warren Pipe and Supply
Lead Free Brass Compression Male Adapters - 5/16"T x 3/8" MIP
LTWFITTING 5/16 in. Flare x 3/8 in. MIP Brass Adapter Fitting (5-Pack) HF485605 - The Home Depot
Amazon.com: Brass Hose Barb Reducer, 3/8" to 5/16" Barb Hose ID, Reducing Barb Brabed Fittings Splicer Mender Union Air Gas Water Fuel Line Heater Garden Pond Poly Tubing Adapter (Pack of 2) :