Toyota 2009 Tundra Owner's Manual page 288

2-5. Driving information
Selecting trailer ball
Use the correct trailer ball for your application.
262
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.