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THE SCREW CASE-BACK OPENER STAKE

The screw case-back opener stake is a bench tool designed for the disassembly and reassembly of the screwed case back of a water-resistant watch case. It follows the classic architecture of the horological stake — a stable base, a vertical column, and a movable head sliding along it — to simultaneously apply, above the case, controlled axial pressure and rotational torque, thereby allowing the case back to be unscrewed without damaging the notches that provide its grip.

In its usual configuration, the head receives, through its lower part, an interchangeable Key whose profile engages with the crown of notches machined around the periphery of the Case back. A handwheel or a lever, acting on the upper operating Screw, applies the downward pressure needed to hold the Key firmly in the notches during rotation. This pressure is essential: without it, the Key jumps from one notch to another and irreversibly scratches or tears the Metal.

At the base of the tool, the watch Case is immobilized in a holder shaped to match the Case middle. These holders, made of soft plastic material — such as polyacetal — or fitted with protective coatings, protect the Case from any marking or scratching from clamping. Centering is critical: the Key must align with the crown of notches, otherwise the slightest misalignment shifts all the force onto a single notch instead of distributing the torque across the whole assembly.

Two families of keys are encountered. Fixed-jaw keys, or profiled keys, are cut to match a precise notch pattern: each reference or each case family then requires its own key. Adjustable-lug keys — generally with three lugs, cylindrical or square — offer superior versatility: the position and spacing of the lugs can be adjusted over a wide range of diameters and notch configurations. It is this latter type that equips the majority of versatile workshop stakes.

In use, the Horologist (watchmaker) immobilizes the Case in the holder, selects and adjusts the Key matching the notches of the Case back, engages it carefully, then applies firm axial pressure before imparting rotation in the unscrewing direction. Pressure must be maintained throughout the rotation, otherwise the Key slips off. The same stake is used for re-screwing at the end of the intervention, a critical step for restoring Water resistance.

Distinct from manual case-back opening tools — rubber-jawed pliers or flat pin wrench — by the rigor of its guidance and the control of force it allows, the screw case-back opener stake became established, with the widespread adoption of water-resistant wristwatches during the 20th century, as an indispensable tool in any bench called upon to work on screw case-back pieces.