An Allen CSK (Countersunk) is a type of screw that features an Allen (hexagonal) drive and a countersunk head. The countersunk design means that the head of the screw is shaped to sit flush with or slightly below the surface of the material when fully tightened, providing a smooth finish. The Allen drive (or hex drive) requires a hexagonal wrench (also known as an Allen key) to tighten or loosen it. ... Allen CSK screws are commonly used in applications where a flush, clean finish is needed, such as in woodworking, machinery, or electronics. The hexagonal drive offers better torque control and reduces the likelihood of the tool slipping during installation. They are typically made from materials like steel, stainless steel, or alloy metals to provide strength and durability.