Round Head Sheet Metal. Counter-Sunk Head Machine. Counter-Sunk Head Sheet Metal. Allegheny is dedicated to providing the most comprehensive line of security nuts, bolts and screws in the industry including the patented Tampruf fasteners. Also known as Tri-Groove. They also carry a wide range of Security Screws such as 6-Lobe & Hex Sockets and a limited amount of Spanners and One-way Screws.