Case Opening Techniques by Case Type

Cases are opened differently depending on their construction, and misidentifying the type before attempting to open one is a common cause of scratched, gouged or bent cases. A screw-back case has a case back threaded directly into the middle case, usually identified by fine knurling around its edge or by small indentations designed to engage a case wrench; it is opened by gripping it (ideally with a purpose-made ball- or die-type case wrench seated in the indentations) and turning counter-clockwise, never by prying, since screw threads are damaged rather than helped by leverage.

A snap-back case, far more common on simpler and vintage watches, is held by spring tension around its rim rather than threads, and is opened by inserting a thin case knife into a small notch usually machined into the case-back edge, then applying gentle, steady leverage to pop the tension seal — a technique that rewards patience and a correctly sized blade far more than force, since a slipped case knife is a frequent cause of scratched case backs and cut fingers.

One-piece cases, in which the entire case is a single shell and the movement is loaded from the front or through a removable crystal and bezel rather than through a back opening, require an entirely different approach: the bezel or crystal retaining ring is released first, often with a specific bezel tool, and the movement, dial and hands are then lifted out as a unit from the front. Attempting to force a one-piece case as though it had a removable back is one of the more damaging beginner mistakes, since these cases have no back seam to exploit at all.

Water-resistant cases of any of these types often add a compressible gasket at the seam, and modern screw-back water-resistant cases in particular can require substantial, evenly applied torque to break the seal without slipping; a correctly fitted case wrench, and a case cushion or holder to immobilise the watch, are standard rather than optional for this work. After any case opening, gaskets are inspected and, in professional servicing, routinely replaced rather than reused, since a compressed or aged gasket rarely reseals reliably.

Because a scratched case or a slipped knife is easy to cause and often impossible to fully undo without refinishing (which itself removes original material), case opening is treated in professional training as a technique requiring the correct tool for the identified type every time, not a skill to improvise with whatever implement is at hand — a caution this lesson extends explicitly to any reader tempted to open a case with a kitchen knife or similar found tool.