Hey all, just wanted to document (if it hasn't been already) the specific sizes required for attaching a ball to the step bumper for doing light duty Class I/II towing (generally 2,000 or 3,500 lbs or less). Maybe I suck at searching, both in the Tacoma manual in my glove box, or on TW (but I think that's due to the fact that 95% of people end up getting a $150 Class IV hitch and attach it to the frame instead). For posterity, here's my truck's specs and the specs of the shank for the bumper:
2011 Base SR5 Access Cab
4x2 4-cyl, no towing package
The bumper on this truck is in the Class II classification, which means a 350lb tongue weight and a max of 3,500lbs of total tow weight (cargo + occupants), so don't worry about getting a ball that does any more than that.
The shank is also crucially important, make sure you order the correct shank diameter (width/thickness) and length, as the generally accepted setup is that at LEAST one thread remains after your washer and nut are secured to the shank on the bumper.
Shank Diameter (B above): 1.0" *
Shank Length (C above - minimum): 3.0" **
(for posterity, A in the graphic above is the Ball Diameter, and D is called the Standard Lift. Thanks to Offroaders.com for the diagram and information)
* The shank diameter is non-negotiable. It's not suggested to try and bore the hole larger, or use a shank that's smaller. The suggested smallest gap should be no less than 1/16", so it's gotta be pretty snug.
** I believe the minimum shank length is somewhere around 2.5" (but if you know the precise minimum here, let me know). Obviously slightly longer isn't unsafe or a bad thing, unless you think it looks like crap, but you must make sure the washer and nut for the shank have enough excess behind them - I believe at LEAST one thread on the shank must be visible below the nut on the shank).
I just ordered a Class II 1 7/8" ball from etrailer.com, who seem to have just about every piece of equipment you'd need for towing. (Just FYI - didn't order this ball because it was Class II, a Class I would have absolutely more than sufficed for what I'm going to be doing, it was the only ball that had the correct diameters and length I need).
Let me know if anything above is incorrect, I'll try to keep it updated. Seems that those of us who use the bumper ball to tow light loads are in the minority (for obvious reasons), but figured I'd provide some clean information for those of you looking.