Why not just try different size metric sockets until you find the one that fits.
Factory plug is 13mm.
The engine coolant drain plug, on a 1998 Ford expedition, is located on the bottom of the radiator. The drain plug will come out by turning to the left.
If it's the "oil" drain plug, the size wrench is, better yet use a socket wrench=13mm.
A wrench
If the drain plug is original equipment, it takes a 17mm wrench or socket.
13mm
15 mm
I have a 96 Camry and the drain plug is metric - I believe it is 14mm. You will need a socket or wrench of the appropriate metric size.
I have a 92 Diamante Wagon. And the drain plug on my car is on the bottom left (driver side). You need a 22mm socket wrench to open it. Hope that helps.
To remove a drain plug, locate the plug underneath the sink or tub, use a wrench to turn it counterclockwise, and then pull it out.
You will need a Torx style bit or wrench to fit into the plug (size T40). A small pipe wrench which grips the outer flange of the plug can also be used to loosen it.
The oil drain plug is right on the oil pan itseft.