Most vintage Omega backs press in or screw in, and a few are held by screws. Some Seamasters have no back at all: the movement comes out through the front. The wrong tool marks gold plate, bends a back or tears the seal. Type the reference from inside the back below to see how Omega's online vintage database lists it, then check the back in your hand before you touch it.
Quick answers
- Where do I start? With the case reference, such as 166.0202. Type it in the box below.
- No notches on the back? Look for a small lip at the edge: that is a press-in back. Some screw-in backs have flats instead of notches and need a die.
- Can I trust the listing? It is Omega's online database, and owners have found errors in it. The watch in your hand wins.
- Can I hurt it? Yes. If the back doesn't move with gentle pressure, stop.
Look up your reference
The reference is stamped inside the back. If you can't open it yet, sellers and old papers often give it. Covers the 1,847 references in Omega's online vintage database.
The back types
| Back | What you see | Tool |
|---|---|---|
| Press-in | A smooth back with a small lifting lip at the edge | Case knife to lift, case press with the right dies to close. Never a wrench. |
| Screw-in | Notches or flats around the edge | Case wrench on the notches, or a die that fits the flats |
| With screws | Small screws around the back | The right screwdriver; keep each screw with its hole |
| Unishell | A solid case with no seam at the back | None: there is no back. Watchmaker job (see below) |
| Sapphire, key-bolt, other | Varies | Leave it to a watchmaker |
Unishell: no back to open
Omega's Technical Guide No. 34 (1966) describes the Unicoc or Unishell case: one solid piece, with no screwed or pressed back. The movement is taken out through the front, after the crown and stem and the glass come out with Omega's extractor. Any photo of a "caseback" on a Unishell Seamaster shows the outside of a solid case. Prying at it only marks the case.
Before you start
Our practice, not a line from Omega's books:
- Hold the case, not the bracelet, in a case holder or on a soft cloth.
- Look at the edge under good light for a lip, notches, flats or screws. That tells you more than any listing.
- Gentle pressure only. If it doesn't move, stop. A stuck back is a watchmaker's job.
- Mind the seal. A back that has been off needs a sound gasket before the watch sees water.
- Gold plate marks easily. Tape the case edge next to where the tool goes.
Opening a watch is at your own risk. We describe what the sources say; we can't see your watch.
The tools
- Case knife: for press-in backs (affiliate links: we may earn a commission)
- Case press with dies: to close a press-in back (affiliate links: we may earn a commission)
- Case wrench: for screw-in backs with notches (affiliate links: we may earn a commission)
- Caseback die set: for screw-in backs with flats (affiliate links: we may earn a commission)
- Watchmaker’s screwdrivers: for backs held by screws (affiliate links: we may earn a commission)
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Opened yours and it's different?
Tell us the reference, what the listing says and what you found, with a photo of the inside of the back if you can: id@watchbreaker.com. We check each one before it goes on the page, and credit you if you'd like.