Timewheel TWJAXW1 Jaxa Type Watch Case Back Opener Wrench for Waterproof Watches Open & close most regular screwd back waterproof watch (up to 35mm case size) The maximum jaw opening is 33mm (Please refer to ASIN: B00944T13U for a XL version) Includes four 4 sets of interchangeable metal chucks: Square, Round, Flat & Knurled Knurled handle prevents loosing your grip Metal chucks are quality made they guarantee not fall off when use