Dimension: M2, M2.5 series screws are often used to fixing keyboard, case, internal parts, M3 series screws are usually used to fixing laptop hard disk. Material: High quality carbon steel, black zinc plated, high hardness, good appearance, environment protection, anti-rust, anti-corrosion, sturdy and durable. Technology: Standard depth and dimension of screw cross slot, flat and smooth screw section without residual burrs, clear and tidy thread without gap.