Lock washers prevent nuts and bolts from turning, slipping and coming loose due to vibration and torque (rotation). Helical (coil-shaped) spring lock washers are most commonly used as they apply greater bolt tension per unit of applied torque. A Belleville washer is a type of spring shaped like a washer. It is the cone-like shape that gives the washer a spring characteristic. Used in conjunction with lock nuts, hex nuts and/or head cap screws, the locking mechanism of a lock washer remains formidable.