http://www.sexuality.org/l/sex/handball.html

That site deals with anal fisting but most of the same rules should apply to vaginal fisting with the exception of what kind of lube you use. With anal fisting a petroleum based lube is ok. With vaginal fisting uless you have a strange desire to also have a yeast infection or something worse water based lubes are the only thing you should even think of using.

Or you could look at this site that deals specifically with vaginal fisting. http://www.sexinfo101.com/as_fisting.shtml

The most I have ever been able to get in is four fingers and most of my thumb into my wife. I have never been able to get my hand in. I think we would have better luck with anal fisting since the pubic bone doesn't get in the way of penetration and from what I have read the sphincter muscles have the ability to expand further then the birth canal, but I have never been able to convince my wife to try it.