Jaxa Style Watch Case Back Opener for Screw-on type Watch Cases Known also as a Key for Waterproof Watches with a screw-on watch case back, maximum jaw opening is 33mm Jaxa Style Case back opener measures 5.7" long with a handle 2-3/8" long Four types of pins/bits for case backs with Polygon, Knurled, Round, or Multi-knotched Includes Wooden case with a front latch closure. Great Tool for Watchmakers, Jewelers, Hobbyists, Enthusiasts who change watch batteries or open watch cases for repairs/adjustments