The tool I use for loosening and tightening tranny drain and fill
plugs is made of a ~M10 bolt which has a 17mm head and three or four
M10 nuts screwed onto it with lock washers. Place the head of the bolt
in the fill plug and then use a 17mm spanner er, wrench on one of the
nuts at the other end of the bolt - costs less than $1 Canadian.
Regards, Mike