DS EN 4131:2009 Aerospace Series - Bolts, Normal Hexagonal Head, Coarse Tolerance Normal Shank, Medium Length Thread, In Heat Resisting Nickel Base Alloy, Aluminium Ivd Coated - Classification: 1250 Mpa (At Ambient Temperature)/425 Degree C Defines the characteristics of bolts, normal hexagonal head, coarse tolerance normal shank, medium length thread, in heat resisting nickel base alloy, aluminium IVD coated.