Flat head socket cap screws are ideal for applications in which there is not enough space to maneuver wrenches or sockets and have an internal-wrenching drive, with a flat top and coneshaped bearing surface. The length of flat head screws are measured from the tip to the top of the head. Black oxide has minimal corrosion resistance. Property class 12.9: Tensile strength: 1,220 MPa or about 176,900 p.s.i. Head marking 10.9. Made from alloy steel, quenched and tempered.