Later edit: I was wrong. Looking over HeelSpur's two posts, he was asking about the pliers after all. Sorry.
We're wandering off course. HeelSpur's asking about the wrench, not the pliers. The top wrench in the photo has a countersunk hole in it. The pliers were probably included in the photo just for entertainment value.
I've seen - well, actually, I've got - automotive wrench sets with a hole in the middle, the whole set held together by a bolt and nut. That way, instead of losing individual wrenches in the mess in the trunk, you could lose the whole thing. Much neater. But the location, and the countersink, make me think that's not the purpose of this hole. I am mysticated.