3/8" X 3/4" Comp X Mip Adapter Brass Fittings 18191 (Pack Of 10) | eBay
Compression Fitting, Generic, 1/4"mpt x 3/8" Tube, Plastic - Walmart.com
Threading Adapter, NPT 3/8 Male to G 1/4 Female
PEX Pipe Fitting, Quick Connect Adapter, 3/8 OD x 3/8-In. MPT - Murfreesboro, TN - Kelton's Hardware & Pet
Amazon.com: PureSec 3/8 to 1/4 inch Straight Union Connector/Reducer Plastic Quick Connect Fittings for RODI System (10, 1/4" to 3/8") : Everything Else