Rudder Cam fitted to the Rudder Stock to keep the tiller down.
If this has broken check that you still have the spring and spring cup that fits under the cam, these often fall out if the cam breaks.
If you also use a pin to secure the tiller down then you will need to drill the cam once the rudder has been set up, it is best to use the rudder a few times first before you drill the hole to ensure everything has settled. When drilling the hole drill from each side to minimise the risk of misalignment.