I mean - fisting? Is fisting not the word you were looking for? I hadn't ever distinguished between fisting with a soft hand a fisting with, well, a fist.

Er, to define my terms: fisting is the insertion of the whole hand into the vagina or anus. In vaginas, there's only so far you can go, but in the right ass you can pretty much get elbow deep. The hardest part on a vagina is getting the knuckles through the pelvic floor muscle and pelvic bones. I don't know what the hardest part of anal fisting is.