There really is no mystery to this. Try this, go to the gym take your middle and ring fingers around a chin-up bar and see if you can hang and hold your own weight by them. Bet ya you can (unless you are very overweight).
Those two fingers can bear much more weight then you think, the lifting power comes from your arms all the fingers have to do is be able to bear the weight. Now divide this weight by 6 people. When I was young, this was a popular thing at boy scout camps doing trust exercises. There is no magic to it, just simple physics.