"M8 Socket Head Bolt (Allen Head Bolt), Socket cap screws are high-strength tension fasteners designed for clamping assemblies and are commonly used in tool and die fixture applications.
Socket caps have a small cylindrical head with tall vertical sides. 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.
Depending on the total length of bolt, thread length may vary. To drive these types of bolt, you will need a Allen Key/Hex Key."