A Woodruff key is a finely machined metal piece used to connect a rotating device to a shaft. The distinction of a Woodruff key is that it is machined to fit into a semi-circular pocket, which eliminates the necessity of cutting or milling a keyway the length of a shaft, greatly increasing the strength of the shaft. It was created by W.N. Woodruff of Connecticut in the late 1800s. In 1888, W.N. Woodruff was awarded the John Scott Medal by the Franklin Institute for the invention of what would forever be known as the “Woodruff key.”
A Woodruff key and its corresponding keyway in the crankshaft of a Yamaha XT250.