I am also quite surprised with the lack of familiarity, especially on this site. Yes, vaginal fisting is more common than many of you realize. Generally, it requires extensive foreplay, lots of lube, and working up to it. Generally, the hand is NOT a fist, but with fingers extended straight, and the thumb and fingertips coming together, in somewhat of a point. This minimizes the width of the knuckle ridge as much as possible. And generally, it is not like using a cock or a dildo. You don't just plunk it in, then pump it in and out. It takes time to get in, and once in, the motion tends to be very subtle and fairly slow. The super-intense sensation of the fullnes makes up for the relative lack of motion. Some like it, some don't. Some can take it, some can't. Once again, one of those things. Whether vaginal or anal, it should ALWAYS be done with a glove on - even the tiniest hangnail can cause tears and abrasions, leaving an inway for infection. But done properly, almost any vagina or anus could accomodate a small or maybe even average hand.