If your truck did not come with arm rests, you will not have the factory square nuts that are pressed into the door to hold the arm rests on. You need to go to the junk yard and get 4 of those nuts which have a press on snaps attached to them. Once you get those, as one of the other responses said like Markeb, put a couple of screws in an mark the inside panel. Note: the arm rest screws go in at about a 30 deg. angle to the door.