Identify the case-back type
Before opening a watch you must identify the case-back type. Three families exist: the snap-on back, the screw-down back and the back secured with screws. Method and tools differ for each.
Snap-on case-back
Identification
The back is smooth, with no notches or visible screws. A small lip or indentation sits along the rim for prying. A loupe is often useful to spot it.
Opening
Slip the blade of a case knife or a case-back lever into the lip. Apply a gentle twist: the back pops off. Work on a soft pad to protect the crystal.
Screw-down case-back
Identification
The back shows evenly spaced notches around its rim. These notches receive the pins of a wrench.
Opening
Three possible tools:
- Jaxa wrench with three adjustable pins, the most versatile.
- Ordinary case wrench with standardised bits.
- Ball opener by friction, for case-backs that are not seized.
Set the pins in the notches, hold the watch in a watchmaker's vice and unscrew counter-clockwise.
Screwed case-back
Identification
Small screws (usually 4 or 6) are visible around the rim. They hold a plate that closes the case.
Opening
Use a watchmaker screwdriver of the correct width. Unscrew in a cross pattern to avoid skewing the back. Keep the screws in a magnetic cup.
Required tools
- Case knife or case-back lever
- Adjustable Jaxa wrench
- Ball case opener
- Watchmaker screwdriver set
- Watchmaker's vice
- x5 loupe
Browse our selection of watch opening tools.
Opening a watch without the right wrench means marking it forever.
Case-back type comparison
| Case-back type | Required tool | Level |
|---|---|---|
| Snap-on back | Case knife | Easy |
| Screw-down back | Pin wrench or universal wrench | Intermediate |
| Back with visible screws | Watchmaker screwdriver | Easy |
Common mistakes to avoid
- Forcing a screw-down back without the proper wrench (risk of scratches)
- Working without an anti-slip surface
- Re-using a broken gasket after opening
FAQ
How do I tell whether a back is snap-on or screw-down?
A snap-on back is smooth with a lip. A screw-down back shows evenly spaced notches.
What if the Jaxa wrench slips?
The back is seized. Apply a little penetrant around the rim, wait a few minutes, then try again with the pins firmly tightened.
Must the gasket be replaced at every opening?
Not systematically, but it must be checked. See replace a case-back gasket for the procedure.
Can a watch be opened without a dedicated tool?
Not advisable. An unsuitable tool scratches the case and risks damaging the movement.