"M3 Counter Sunk Bolts caps have a small cylindrical head with tall vertical sides. Depending on the total length of bolt, thread length may vary.
It has hexagonal socket in the head (internal-wrenching hexagon drive) which is used to drive the bolts and screws using a Hex Key or Allen Key. To drive these types of bolt, you will need a Allen Key/Hex Key.
M3 Counter Sunk Bolts are high-strength tension fasteners designed for clamping assemblies and commonly used in tool and die fixture applications."