StarSide Professional JAXA Type Watch Case Back Opener Wrench for Waterproof Watches Regular size Open & close most regular size (up to 35mm ) waterproof watch cases The maximum jaw opening is 33mm Includes four 4 sets of interchangeable chucks: Square, Round, Flat & Knurled Knurled handle prevents loosing your grip Wrench comes in a yellow storage box that holds all pieces.