A peg or feather key is a type of key that is similar in function to a Woodruff key. It is used to secure a rotating component to a shaft, typically in applications where high torque loads are involved. The key is a rectangular or square metal piece that is inserted into a keyway or slot that is machined into both the shaft and the component. The key has a projecting tab, or "peg," that extends out from the edge of the key and fits into a corresponding slot in the component. This helps to prevent the component from rotating independently of the shaft.