240DE – 5/16 X 3/8 Female Inverted X Male Inverted Flare – Couplings Company
Lead Free Brass Compression Male Adapters - 5/16"T x 3/8" MIP
3/8" Male NPT x 5/16" Flare (SAE) Brass Adapter
LTWFITTING 5/16 in. O.D. Comp x 3/8 in. MIP Brass Compression Adapter Fitting (5-Pack) HF685605 - 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) :