Not only do these have the strongest hold of all the flange nuts we offer, they are also manufactured and tested to strict U.S. military standards for material and construction. They have irregularly shaped threads that grip the screw to resist loosening in high-vibration applications. The threads prevent the nut from backing out, but they also increase the effort to install and remove. To get these nuts off, you may need special tools, such as an impact wrench or propane torch, so they are not reusable. Nuts have a flange that distributes pressure evenly across the mounting surface without the need for a separate washer. They are ideal for securing screws in oversized or irregularly shaped holes since the flange covers a larger area than standard nuts. Also known as collar nuts.