A lock washer is designed to prevent a secured joint that is fastened with a bolt or screw from turning or loosening, in response to shock or vibration. It can have internal or external teeth for gripping, and can be split through one part of the ring. Split, star, and tab lock washers are commonly used in airplane manufacturing. They are made for various bolt sizes, and are selected for their inner and outer diameter, and thickness. Commonly made of steel or stainless steel, a lock washer can have a finish such as cadmium or zinc.