Amazon.com: Appli Parts Brass 1/4 inch Compression Fitting reduction coupling for in line water filter with Male 3/8 inch NPT connection for Copper or PVC tubing APWF-100BC
SharkBite 1 Inch CTS x 1 Inch PVC Transition Coupling, Push to Connect Brass Plumbing Fitting, PEX Pipe, Copper, CPVC, PE-RT, HDPE, UIP4020A - Amazon.com
SharkBite 1/2-in Push-to-Connect Coupling in the Push to Connect Fittings department at Lowes.com
NIBCO 1/2 in. CPVC-CTS and Copper Alloy Lead-Free Slip x Compression Union C4733-7-LF - The Home Depot