ice maker hookup (5/16" and 1/4")

[zhtst]

I bought a refrigator with ice maker. The delivery man could not hook the water line (5/16" threaded male connector) with ice maker (1/4" threaded male connector) using 1/4" copper line. He said my water line connector is not standard size (1/4").

What do I need to buy to connect 1/4" copper tube to 5/16" water line? The water line itself is 1/4", just the outside diameter is 5/16".

Thanks in advance for your help.

Tom