1.√ Dimension: Total 815 pieces M3 x 8/12/16/20 mm, M4 x 8/12/16/20 mm, M5 x 8/12/16/20 mm, M6 x 8/12/16/20 mm black button head socket cap screws with matching nuts, lock washers and flat washers, different sizes and enough quantities can meet your different daily needs. 2.√ Material: M3 M4 M5 M6 black button head socket cap screws nuts washers kit are made of high quality 10.9 grade alloy steel, which have high strength, not easy to deform, corrosion resistance and wear resistance in bad environments, which can ensure a long time using. 3.√ Functions: M3 M4 M5 M6 black button head socket cap screws are commonly used in machinery, it mainly has the advantages of easy fastening, disassembly, and not easy to slip corners. The head of button head socket cap screw is round, and the middle is a recessed hexagon. It is usually used with hex wrench (hex wrench is included). 4.√ Widely Applications: Commonly used in machine assembly, especially for removable panels and parts, suitable for all kinds of precision machinery industry, classified instruments, instruments, electronic products, printed projects, household appliances, communication products, locks, lamps, lights, toys, etc.