that is the firing pin return spring, imagine the bolt with the end towards you, the chamber face away from you, there is a small dowel pin that goes through the bolt left-to-right (of vice-versa) it holds the firing pin in place, that small spring with a bent piece of metal sits under the firing pin, the small metal piece braces againts a small cutout in the firing pin channel, and the spring itself will place tension on the firing pin when in place, in short it keeps the firing pin from hitting the primer of a round, or the chamber face if dry fired or dropped. i will try to get a picture for reassembly, and no it is part #11 and 12. hope this helps.