Lock pin used to lock the tiller / top stock to the lower stock.
Fits through the top stock and rudder cam.
This version of the pin is a stainless steel (A2) split pin.
Note - if drilling the hole through the top stock and cam it is advisable to drill from each side of the top stock to allow for any mis-alignment when drilling. Also make sure you have the rudder set up exactly as you want it before drilling the cam.