A selectively hardened nail includes a nail head, an elongated shank, and a tip. A portion of the nail shank is made harder than the remainder by selectively heat treating that portion, and cooling it. The nail has controlled bending properties. The selectively hardened portion does not significantly...http://www.google.com.au/patents/US6086305?utm_source=gb-gplus-sharePatent US6086305 - Nails having selected heat treatment and hardening
