If your 1/2-13 female threads in the frame of your car are dirty, rusty, or damaged by weld spatter or whatever, you can file a vee in the first few threads of your bolts so that they are cutting like a tap. Make the side of the vee about 90 degrees to tangent in the clockwise turning direction for best cutting. Since the bolt is not nearly as hard as a tap, it won't cut as well as a tap, but usually well enough to get by. The original bolts had "paint cutter lead points" which do the same thing, as shown in the AMK catalog photos of the B and E body bumper arm bolts.