Allen Hex Drive Size: 4 mm Metric; Package Includes: 50 PCS M5-0.8 x 20mm Diameter of the head: 8.72mm (max), Height of the head: 5.0mm (max); Screw Length: 20mm (excluding the height of the head) Manufactured with a high-precision process; Featured with a cylindrical head and internal hex drive that allows higher tightening torque; Widely used in home, industrial, automotive, constructions, tools, laptops, 3D printers, both indoor and outdoor applications; The flush head provides a clean look when installed Thread: Full Coverage; Thread Pitch: 0.8mm; Color: Black Made of grade 12.9 alloy steel which provides good strength and ideal use in indoor projects; if you hope to use them in environments with mositure, please choose stainless steel 304/316 because black oxide finish is not a protective finish and will rust when exposed to mositure environment Socket head cap screws are precision threaded fasteners with an internal hex drive also called allen hex drive.They are known for their effecient application performance and endurance widely used in a variety of industries such as construction, manufacturing, engineering, assembling and so on. The 12.9 grade alloy steel provide perfect strength and good corrosion resistance in bad environments like high temperature, cold weather and high humidity areas without the need for time consuming and costly maintenance.