They contact the flat surfaces of a bolt head or nut versus the pointed parts so they can be used on nuts that have been rounded off. They work better on rusted fasteners but sometimes they still will not remove them without help from heat or whatever. I swear by them.What is special about these minus the ability to be used on both? Are they good for rusted fasteners? I first heard about them ~10 years ago from a junkyard employee who swore by them.