So how do you know which one to buy? Take your BMW screw and use the small sharpie marker. Count and mark each tooth/burr. As for the quality of the instrument. It is MUCH better than the OEM key which is cast metal. So you can twist it and bend the wedges. This tool looks like chrome molybdenum or a VERY dense metal. That is hard. I bought two, one for my trunk and one for my tool box.