Small swiveling rudder hold down. Installed above the top pintle when the rudder is on the boat. It prevents the rudder from lifting out of the gudgeons during a grounding or in the event of a capsize.
Install with a little blob of silicone or a small rubber o-ring to prevent it from just twirling around. It should stay put when rotated in order to funtion properly.
Do not mount it too close to the pintle, make sure it will be able to rotate when installed.