Toyota 4runner 2009 User Manual page 218

2-5. Driving information
Selecting trailer ball
Use the correct trailer ball for your application.
220
Trailer ball load rating
Matches or exceeds the gross
trailer weight rating of the trailer.
Ball diameter
Matches the size of the trailer
coupler. Most
stamped with the required trailer
ball size.
Trailer Typical trailer ball
class size
IV
II and III
I
Shank length
Protrudes beyond the bottom of
the lock washer and nut at least 2
threads.
Shank diameter
Matches the ball mount hole
diameter size.
couplers are
2 5/16 in.
2 in.
1 7/8 in.