The fastener of the present invention has a head integrally formed with a threaded shank. The face of the head has a triangular recess with a triangular centerpost extending upward from the recess. The recess has three sides forming corners, and the centerpost has three sides forming apices. The walls...http://www.google.de/patents/US6186718?utm_source=gb-gplus-sharePatent US6186718 - Threaded fastener having a head with a triangle centerpost within a triangle recess
