Case back tool

A case back tool opens the back of the watch, which you need for a battery change, a seal check or a movement inspection. This is not a band job, and it is the one category on this site where the wrong move risks the movement, not just the looks. Treat it accordingly.

Three case back types, three different tools

A snap-on back has a small lip and is opened with a case knife or a ball-style press, levered at the notch only. A screw-on back has cut-outs or flats and needs a two- or three-pin wrench, the Jaxa type, set to the exact spacing, or a die holder for coin-edge backs. A screw-down back held by tiny screws around the rim needs the correct small screwdriver, nothing else. Using a knife on a screw-on back is the classic way to send the blade across the back, the bench and sometimes the hand.

What matters when choosing

Grip and adjustability over accessory count. The pins of a Jaxa-type wrench must sit fully in the cut-outs and the wrench must lock at that width, or it cams out and scars the back. A back you will open often, like a battery quartz, justifies a better wrench than a watch you open once.

Two things people underestimate

The gasket and water resistance. Every time the back comes off, the rubber gasket should be inspected and re-seated, and water resistance is not guaranteed again without a pressure test. And torque on closing: a screw-on back done up by feel is either not sealed or over-tightened. If the watch matters or has any water rating you care about, the open-and-reseal job belongs with a watchmaker, not a kitchen table.

This category supports your battery and service jobs, not band sizing. For band work, see the link removal and spring bar categories.

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