Recently I have started to test my Girlfriends limits. It started at a few trips to the local sex shop and we have been slowly buying larger toys. I have been trying the last few weeks to fist her and for the most part she is taking it well. Although I am short, 5'6" I have large thick hands and am having a problem getting past my knuckles. I am making sure that I start slow, I usually get her going by going down on her. I use three fingers to start spreading her open and I increase to four. I apply a generous amount of lube and I attempt to insert the fist but I get caught up at the knuckles. She keeps asking for more and I try but I don't want to hurt her. I think I am doing it right but, any one have any tips?