US Patent 7740436 Clinch nut

A metal clinch fastener has portions thereof selectively hardened to enable use of the fastener with metal members of differing hardness values. The selective hardening of the fastener enables mounting with application of required forces for piercing and/or plastic deformation of the metal member without undesirable deformation or distortion of the fastener. The screw thread region or zone of the fastener has a relatively lesser hardness suitable and may be pre-threaded or later threaded by engagement with a thread forming screw.