This Watch back case opener set is designed to open Rolex, Tudor or other grooved, waterproof Oyster case back without having run away error that might result in scratching your precious watch case. You'll get the peace of mind that the right tool will not damage the ridges pm the back case cover.  <br><br><strong>Set A Case Back Size Diameter (6 Dies):</strong> <br>No 0: 18.5 mm <br>No 1: 20.2 mm <br>No 2: 22.5 mm <br>No 3: 26.5 mm <br>No 4: 28.3 mm <br>No 5: 29.5 mm<br><br><strong>Set B Case Back Size Diameter (7 Dies): </strong><br>No 0: 18.5 mm <br>No 1: 20.2 mm <br>No 2: 22.5 mm <br>No 3: 26.5 mm <br>No 4: 28.3 mm <br>No 5: 29.5 mm<br>No 6: 36.5 mm (XL)