My 751 key is for the "basement" storage doors on either side and for the front generator storage door. The square black FIC keys are for the side entry doors, one key for each door lock set. The EZSET (house key) is for the garage/living area door. At least this is the setup on my 09 3912. I changed the entrance doors so they are all keyed alike, it cost me $24 at a local locksmith, he just ordered the locksets from his own vendor.