Woodruff key, 4 x 5 mm TV Series 1 flywheel
This woodruff key is used to line up the flywheel when you fit the flywheel to the crank. Contrary to popular belief it does not stop the flywheel spinning on the crank, only the grip of the taper on the flywheel does that. If you find you are burning through a lot of woodruff keys it's possible you are not tightening your flywheel enough or the key way is damaged.
4 x 5 mm