A threaded fastener such as a weld nut or a weld stud has a projection from a surface thereof, with the projection bearing a thread. A weld ring substantially surrounds the threaded projection. In a fastener system using the fastener, a mounting structure has a keyhole including a larger diameter hole and a narrower diameter slot. In the assembly, a portion of the weld ring projects into the slot to resist rotation of the fastener relative to the mounting structure.