Please, if you are using some book on the Mauser, forget it. I repeat, that is NOT a Mauser bolt and attempting to follow instructions for a Mauser will only get you confused. The only similarities to the Mauser are the long extractor and the bolt stop in the receiver.
Hawg, that pin is the trigger interlock, common on cock-on-close actions (there is one on the M1917 Enfield). It prevents unlocked firing by keeping the trigger from being pulled if the bolt is not fully closed and locked.