Open a 1960s Constellation with a date and you will often find a calibre 564. Open a Seamaster from the same years and it is often a 565. They look the same under a loupe, and in Omega’s own catalogue they nearly are: both arrived in the 1966 supplement to GF 620-3, both are printed as difference sheets against the 563, and 109 of their part numbers are the same. Here is what actually separates them, and why it matters when you buy one or hunt parts for it.
Quick answers
- The difference: the 564 is the chronometer execution (“bulletin” in Omega’s designation), and each has its own train wheel bridge, 564.1003 or 565.1003.
- The same: 24 jewels, 19,800 an hour, 27.90 × 5.00 mm, the date corrector, and the 563 base.
- Parts: 109 part numbers are listed for both. Buy by the number, not by “Constellation” or “Seamaster”.
- Which is yours: read the train wheel bridge, then check the reference inside the caseback.
Side by side, from the catalogue
| 564 · Constellation | 565 · Seamaster | |
|---|---|---|
| Omega’s designation | 27.90 RA SC PC CAL CORR AM bulletin 24 p. | 27.90 RA SC PC CAL CORR AM 24 pierres |
| Chronometer (bulletin) | Yes | No |
| Jewels | 24 | 24 |
| Beat | 19,800 an hour | 19,800 an hour |
| Size | 27.90 × 5.00 mm | 27.90 × 5.00 mm |
| Date corrector (CORR) | Yes | Yes |
| Built on | 563 | 563 |
| Catalogue | GF 620-3 supplement, 1966 | GF 620-3 supplement, 1966 |
| References in Omega’s records | 15 Constellations, 1962 to 1971 | 22 Seamasters, 1962 to 1975 |
Designations, jewels, beat and size: GF 620-3 and its 1966 supplement. Reference counts and years: Omega’s vintage database.
What the part numbers show
Omega printed both calibres as a short list of changes on top of the 563, so most of each movement carries somebody else’s number. Counted the same way for both:
| Part numbers | 564 | 565 |
|---|---|---|
| Its own number (the train wheel bridge) | 1 · 564.1003 | 1 · 565.1003 |
| Carry a 563 number | 19 | 22 |
| Carry a 550, 551 or 552 number | 34 | 35 |
| Carry a 560 number | 7 | 24 |
| From older calibres (470, 330, 100 and others) | 15 | 15 |
| Screws | 22 | 22 |
| Jewels | 11 | 11 |
| Bushings | 2 | 2 |
| Part numbers in all | 111 | 132 |
The one number each calibre owns is its train wheel bridge, and that bridge is where the calibre is stamped. The 565’s longer list is mostly date work: it carries 24 numbers from the 560 against the 564’s 7, among them date wheels coded for the stem and window position (560.1586A, 560.1587A/J, 560.1590A). A coded wheel belongs to a movement turned in its case, so it should suit the case.
One printing error to know about, so you don’t chase it: Omega prints the 563 date indicator driving wheel as both 563.1564 and 563.1560. It is the same part, so search both.
The chronometer: what “bulletin” buys
“Bulletin” marks the chronometer execution, rated and certified. The 564 carries it; the 565 does not. Nothing in the parts list explains the difference: the 564 owns one part, and so does the 565. The chronometer premium is paid for adjustment and paperwork, not for different metal.
That is why the Constellation, Omega’s chronometer line, took the 564. Omega’s records list 134 mechanical Constellation references, 101 of them certified chronometers. But not every Constellation is one, and the 564 is not only a Constellation calibre: Omega lists three Seamasters with it, BA 368.0831 (1966), ST 168.0024 (1969 to 1972) and ST 168.0050 (1970 to 1976).
Which one is in your watch
- Read the bridge, not the listing. On this family the calibre number is stamped on the train wheel bridge. Sellers copy the calibre from an old listing more often than from the movement.
- Check the reference. It is inside the caseback. The Constellation guide and the Seamaster guide list the calibre Omega gives for every reference. A 565 in a case built for a 564 is a marriage.
- Watch for “or”. Omega lists some 1962 references with two calibres: Constellation 168.0005 and 168.0010 as 561 or 564, Seamaster 166.0002 and 166.0003 as 562 or 565. The 564 and 565 sections are dated 1966, so on a reference first made in 1962 the older calibre came first. The serial number lookup tells you which era yours is from.
- Try the date. Both have the corrector. Pull the crown to the first click and turn: the date should jump. If it doesn’t, it may be a 561 or 562, which have none.
Hunting parts: the swap rule
Because 109 numbers are shared, a part pulled from a Seamaster 565 can be exactly right for a Constellation 564, and the other way round. The rule is simple: match the Omega number, never the calibre or the model name on the listing. The bridge is the one part that is not shared, and the bridge carries the calibre number, so a 565 bridge in a 564 makes a movement that reads as the wrong calibre. The parts finder shows every calibre a number fits, and the 565 parts page lists the ones people hunt.
Take both apart
Both are on The Bench, free in your browser: every part and screw with its Omega number on screen, taken off in bench order and built back up. Do the 564, then the 565, and the shared parts will look familiar the second time.
Play the 564 BenchPlay the 565 Bench
Questions
What is the difference between the Omega 564 and 565?
Two things. The 564 is the chronometer execution: Omega prints “bulletin” in its designation, and the 565’s has none. And each has one part of its own, the train wheel bridge, 564.1003 or 565.1003, where the calibre number is stamped. Both are 24 jewels, 19,800 an hour, 27.90 × 5.00 mm, with the date corrector, built on the 563.
Is a Constellation part the same as a Seamaster part?
Often. 109 part numbers are listed for both the 564 and the 565. Hunt by the part number, not the calibre or the model name: a part sold as “565, Seamaster” is a Constellation 564 part if its number is on the 564’s list.
Is every Constellation a chronometer?
No. Omega’s records list 134 mechanical Constellation references and 101 of them as certified chronometers. The chronometer movement is the bulletin one: the 551, 561, 564, 1001, 1011 and 1021 carry the word or BULL in their designations.
Are there Seamasters with the 564?
Yes. Omega’s records list BA 368.0831 (1966), ST 168.0024 (1969 to 1972) and ST 168.0050 (1970 to 1976) as Seamasters with the 564, automatic chronometers. The reference inside the caseback decides which calibre belongs.
How do I tell which one is in my watch?
Read the number on the train wheel bridge, not the dial or the listing. Then check the reference inside the caseback against the calibres Omega lists for it. A 565 in a case built for a 564 is a marriage.
Not sure what is in yours? The Movement ID report is US$75: the calibre read from the bridge, checked against the case reference and Omega’s catalogues, with nothing to pay until we confirm your photos can answer it. The 560 to 565 data sheet is free.
Sources: Omega GF 620-3 and its 1966 supplement; Omega’s vintage database for references and years; Omega technical guide TG-19-C-097. Watch Breaker is not affiliated with, endorsed by or connected to Omega SA or the Swatch Group. Omega, Constellation and Seamaster are trademarks of Omega SA.