A black M8x30 DIN 7991 hexagon socket screw is a countersunk screw with a conical head that sits flush with the surface it's fastened into, a metric thread of 8mm diameter and 30mm length, and a hexagonal socket for tightening with an Allen key. The "black" finish is typically an oxide coating for corrosion resistance and a smoother, more professional appearance. 

Specifications and features

• Type: Hexagon socket countersunk head screw
• Standard: DIN 7991 (also known as ISO 10642)
• Thread: M8 ($8$mm diameter), 30mm length
• Head: Countersunk, conical, designed to be flush with or below the surface
• Drive: Hexagon socket, requiring an Allen or hex key for installation and removal
• Finish: Black, typically a black oxide coating, providing corrosion resistance and a smooth look
• Material: Often made of high-tensile steel (e.g., grade 10.9) for strength, but can be stainless steel
• Applications: Used in situations where a smooth, flat surface is needed, such as machinery, equipment, automotive parts, electronics, or woodworking and DIY projects