8.8 Nickel Plating Socket Cap Self Tapping Screws Carbon Steel Allen Key Tappers. Thread diameter : M4 M5 M6. Thread length : 8mm – 60mm. Product size = thread diameter x thread length (length measured from the lower part of the head). Strength: Grade 8.8. High strength carbon steel grade 8.8, high toughness, good hot and cold workability, excellent machinability, etc. Grade 8.8 bolts, commonly known as high strength bolts, are suitable for steel frame structure beam and column connections, solid web beam connections, heavy crane beam connections in industrial plants, braking systems and connections to important structures subject to dynamic loads. Thread diameter – M4 (4mm). Head diameter : 7.22 – 6.78 mm. Head thickness : 4.0-3.82mm. Thread diameter – M5 (5mm). Head diameter : 8.72-8.28mm. Head thickness : 5.0-4.82mm. Thread diameter – M6 (6mm). Head diameter : 10.22-9.78mm. Head thickness : 6.0-5.70mm. Length does not include head.