DS EN 3323:2009 Aerospace Series - Bolts With Double Hexagon Head, Relieved Shank, Long Thread - In Heat Resisting Steel Fe-Pm 38 (Fv 535) - Classification: 1000 Mpa/550 Degree C Defines the characteristics of double hexagon head bolts with relieved shank and long thread in heat resisting steel FM-PM 38, tensile strength class 1000 MPa at room temperature.