Greetings!

I currently drive a 94' Montero but just recently the engine began to have problems. Upon further inspection, I noticed that one of the spark plugs was unplugged. I just need to tighten it back up to get the engine running fine again but I can't seem to find the right socket size for the plug. Does anybody know the socket size for my car model? I can't seem to find it anywhere and I need it to be able to tighten the plug properly. Thanks in Advance!