I purchased this wrench to help me open the backs of two watches: a Wenger Swiss watch and a Polar heart rate monitor watch.  The wrench fit both watch cases.  However, it was still somewhat difficult to open them because I did not have a special vise to hold the watches in.  The wrench works better than other methods I had tried (e.g., tips of needlenose pliers).  It is a heavy, solid wrench and the different size tips are easy to swap out.