Spark plugs come in three sizes: 5/8, 3/4, and 13/16. I think the RJ19LM takes a 13/16 socket. However, it would be wise to have all three sizes of sockets in your tool box - you never know when you will need one or the other.
I think that uses a 7mm Allen wrench.
If it's the "oil" drain plug, the size wrench is, better yet use a socket wrench=13mm.
Probably about a 15 millimeter wrench or socket.
15mm six point socket or 15mm wrench
17 mm socket or boxed in wrench.
I believe it a 1/2 " socket or wrench.
use an Allen wrench not a socket or open or box wrench.
14 or 17 mm socket.
You need a fitting socket, a socket wrench and an extender. Anyone who works on his own car will have a set.
Oil drain bolts on most vehicles vary from 7/16 to 5/8. Take a crescent wrench under with you to check, then compare the size to a regular socket and use it.
7/16 wrench 24mm socket 9/16 wrench 3/4 wrench
A 5/8" socket wrench.