5/8 inch
If it's the "oil" drain plug, the size wrench is, better yet use a socket wrench=13mm.
The wrench size is 14mm.
13mm
5/8
Factory plug is 13mm.
My 92 has a 9/16 size plug My 1997 LeSabre has a 15mm drain plug.
13 mm13 mm
The oil drain plug uses a 13 mm wrench.
The original engine oil drain plug wrench size should be 15mm.
If the drain plug is original equipment, it takes a 17mm wrench or socket.
15mm
The wrench size should be 15mm.