M8 Hex Bolt/Setscrew Fully Threaded Dimensions - M8 x 40 Bolts Here is what the dimensions mean… M - Metric thread 8 - Diameter of the bolt, in millimetres 40 - Length, in millimetres (from the base of the bolt head to the end of the thread) Material Zinc Plated Steel - A Corrosion-Retardant plating provides protection from external elements and extends the life of the metal used to make these M8 40mm bolts. Specification M8 Bolts 40mm DIN933 Grade 8.8 Available in a variety of sizes; M8 x 25mm, M8 x 30mm, M8 x 40mm, M8 x 50mm