Timewheel TWJAXA2 Waterproof Watch Screw Case Back Opener Wrench for Large Watch With 4 Sets of Champs (Round, Flat, Square & Toothod) Imported Open & close most screw waterproof case back size up to 55mm Includes four 4 sets of interchangeable metal chucks: Square, Round, Flat & Knurled The maximum jaw opening is 53mm Knurled handle prevents losing your grip Metal chucks are quality made they guarantee not fall off when use