Sumnacon Large Watch Case Opener Tool - JAXA Type XL Battery Replacement Wrench Watch Back Remover With 4 Sets Of Interchangeable Chucks for Most Screw Large Waterproof Watch Case Backup (Extra Large) The maximum jaw opening is 52mm. Knurled handle prevents losing your grip Includes four 4 sets of interchangeable chucks: 3 x Square & 3 x Round & 3 x Flat & 3 x Knurled Designed to remove the back lid from watch without marks or scratched Easily adjustable for various case dimensions Open & close most screw waterproof case back up to 55mm case size