Omega Bumper Automatic: Which Calibre Is Inside

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Shake an early automatic Omega and feel a soft knock: that is a bumper. The weight swings through part of a turn and bounces off two small springs instead of spinning all the way round. Omega built the family on fifteen calibres, from the 330 to the 355, and its records put 64 references on them between 1943 and 1958, Seamasters and the first Constellations among them. Here is every one, with the calibre that belongs in it.

Look up your reference

Quick answers

The movement: set by the reference. Omega’s records tie 64 bumper references to ten calibres; the 354 and the 342 are the most common.
Two sizes: the 330 to 333 are 30.10 mm across; the 340 to 355 are 28.10 mm.
Seconds hand: small seconds at six on the 330 to 344; seconds from the centre on the 350 to 355. A date window means the 353 or the 355.
Parts: one winding stem, 340.1106, is printed for every 28.10 mm bumper. Buy by the Omega part number.

Every bumper reference, with its calibre

Show the full table (64 rows)

Reference	Omega’s line	Years	Calibre	Case
OJ 2402	—	1943	342 or 344	14K gold
CK 2446	—	1946	351	Steel
CK 2481	—	1946	351	Steel
CK 2493	Seamaster	1949	332	Steel
CK 2494	Seamaster	1949	351 or 354	Steel
CK 2514	—	1949	343	Steel
CK 2576	Seamaster	1949	342 or 344	Steel
CK 2577	Seamaster	1949	351 or 354	Steel
CK 2583	—	1949 to 1958	332	Steel, 35 mm
CK 2635	Seamaster	1949 to 1954	351 or 354	Steel, 32.5 mm
CK 2637	—	1949 to 1954	351	Steel, 35 mm
CK 2657	Seamaster	1949	342	Steel
DW 2482	—	1949	332	Gold-filled
KO 2636	—	1949 to 1958	342 or 344	Gold-capped steel
OJ 2517	—	1949	352	14K gold
OJ 2518	Seamaster	1949	343	14K gold
OJ 2520	Seamaster	1949	352	14K gold
OT 2499	Centenary	1949	343	18K gold
OT 2516	—	1949	352	18K gold
OT 2518	Seamaster	1949	343	18K gold
OT 2520	Seamaster	1949	352	18K gold
OT 2617	—	1949	332	18K gold
OT 2643	Trésor	1949	351	18K gold
OT 2659	Trésor	1949	342	18K gold
G 6518	US model	1950 to 1955	351	14K gold
OJ 2585	—	1950	332	14K gold
CK 2597	—	1951 to 1958	351	Steel, 34 mm
CK 3950	Automatic	1951 to 1954	342	Steel, 30.5 × 30.5 mm
KW 2596	—	1951	342	Steel, gold bezel
OJ 2550	—	1951	351	14K gold
OT 14320	—	1951 to 1954	342	18K gold, 35 mm
OT 2644	Trésor	1951	332	18K gold
OT 3903	—	1951	342	18K gold
CK 2648	Constellation	1952	352 or 354	Steel
CK 2652	Constellation	1952	352 or 354	Steel
CK 2658	—	1952 to 1958	342	Steel, 35 mm
F 6212	US model	1952	342 or 344	Gold-filled
F 6231	US model	1952	342 or 344	Gold-filled
F 6524	US model	1952	342	Yellow gold
G 6213	US model	1952	354	Gold-filled
G 6525	US model	1952	354	Yellow gold
KO 2627	Seamaster Calendar	1952	353	Gold-capped steel
OT 2648	Constellation	1952	352 or 354	18K gold
OT 2700	Constellation De Luxe	1952	354	18K gold
OT 2710	Trésor	1952	351 or 354	18K gold
CK 2766	Seamaster	1953	344	Steel
OT 14324	Seamaster Luxe	1953	352	18K gold
OT 14327	De Luxe Chronometer	1953	352	18K gold
OT 14349	Automatic	1953	340 or 342	18K gold
OT 14355	Constellation Grand Luxe	1953	354	18K gold
OT 2709	Trésor	1953	342 or 344	18K gold
OT 2714	Trésor	1953	342 or 344	18K gold
CK 2663	—	1954	344	Steel
CK 2753	—	1954	354	Steel
CK 2757	Seamaster Calendar	1954	355	Steel
KO 14350	Seamaster	1954	354	Gold-capped steel, 34 mm
KO 2767	Seamaster	1954	351 or 354	Gold-capped steel
KO 2782	Constellation	1954	352 or 354	Gold-capped steel
OG 14326	Chronometer De Luxe	1954	354	18K white gold
OT 14609	Automatic De Luxe	1954	342	18K gold
OT 2736	Trésor	1954 to 1958	354	18K gold, 33.5 mm
OT 2782	Constellation	1954	352 or 354	18K gold
OT 2799	Constellation De Luxe	1954	354	18K gold
OT 3953	Calendar Grand Luxe	1954	353 or 355	18K gold

Omega’s vintage database. A dash means Omega files the reference without a model line. Sizes only where Omega’s record gives them. Where a reference lists two calibres, Omega’s own record names both.

By calibre: the 354 in 19 references, the 342 in 17, the 351 in 12, the 352 in 11, the 344 in 9, the 332 in 6, the 343 in 4, the 353 and 355 in 2 each and the 340 in 1. The first Constellations used the bumper: eight references from 1952 to 1954, all on the 352 or the 354.

The fifteen calibres, from the factory catalogue

Calibre	Omega’s designation	Size	What sets it apart	Part numbers we hold	References
330	30.10 RA PC AM 17 pierres	30.10 × 4.55 mm	The base: small seconds	96	—
331	30.10 RA PC JUB AM 17p	30.10 × 4.55 mm	Chronomètre Centenaire version	96	—
332	30.10 RA PC T1 AM 17p	30.10 × 4.55 mm	T1 regulating set-up	104	6
333	30.10 RA PC T1 RG AM 17 pierres	30.10 × 4.55 mm	T1 with RG regulator	107	—
340	28.10 RA PC AM 17 pierres	28.10 × 4.80 mm	The smaller base: small seconds	96	1
341	28.10 RA PC JUB AM 17 pierres	28.10 × 4.80 mm	Centenaire version	96	—
342	28.10 RA PC T1 AM 17 pierres	28.10 × 4.80 mm	T1	106	17
343	28.10 RA PC T1 RG AM 17 pierres	28.10 × 4.80 mm	T1 with RG regulator	108	4
344	28.10 RA PC T2 RG AM 17 pierres	28.10 × 4.80 mm	T2 with RG regulator	108	9
350	28.10 RA SC PC AM 17 pierres	28.10 × 5.40 mm	Seconds from the centre	109	—
351	28.10 RA SC PC T1 AM 17 pierres	28.10 × 5.40 mm	Centre seconds, T1	116	12
352	28.10 RA SC PC T1 RG AM 17 pierres	28.10 × 5.40 mm	Centre seconds, T1, RG	119	11
353	28.10 RA SC PC T1 CAL AM 17 pierres	28.10 × 6.10 mm	Centre seconds and date	124	2
354	28.10 RA SC PC T2 RG AM 17 pierres	28.10 × 5.40 mm	Centre seconds, T2, RG	122	19
355	not printed in our copy	6.10 mm tall	Centre seconds, date, RG	106	2

Designations and sizes: Omega GF 620-1. Every calibre printed runs at 19,800 beats an hour on 17 jewels. Part counts: the Watch Breaker database today; it grows as more of Omega’s books are loaded.

Reading the designation: RA is automatic winding, SC seconds from the centre, PC shock protection, AM antimagnetic, CAL a date. T1, T2 and RG name different regulating set-ups, and Omega gave each one its own calibre number, which is why there are so many bumpers. JUB marks the Chronomètre Centenaire versions.

Where the bump comes from

In a bumper the oscillating weight does not turn a full circle. It swings in an arc and is stopped at each end by banking stop springs, Omega part 330.1415, which throw it back the other way. The winding parts that make this work sit together in one block of numbers in the catalogue: the oscillating weight axle 330.1400, the weight bearing 330.1403, the pawl-bearing yoke 330.1407, the driving gear for the crown wheel 330.1410, and the impulse and stop clicks with their springs, 330.1411 to 330.1414.

Which one is in your watch

Read the movement. The calibre number is on the movement. Sellers copy it from an old listing more often than from the watch.
Read the reference and find it in the table above, or in the reference lookup.
Look at the seconds hand. Small seconds at six: the 330 to 344. Seconds from the centre: the 350 to 355.
Look for a date. A date window on a bumper means the 353 or the 355.
Check the years. The serial number lookup dates the movement against the reference.

Hunting parts for a bumper

The bumpers borrow heavily from one another, so a part pulled from one calibre often fits several. The winding stem 340.1106 is printed for all eleven 28.10 mm calibres, the 340 to the 355. The parts finder shows every calibre a number fits. Case parts, crystals and bracelets follow the reference: start with the crystal lookup.

Omega bumpers on eBay: For sale now What they sold for Movements and parts (affiliate links: we may earn a commission)

Take one apart

The bumpers are not on The Bench yet. The 565, a later Omega automatic with a full rotor, is: every part and screw with its Omega number on screen, taken apart and built back up, in your browser, no sign-up.

Play the 565 Bench The Seamaster guide

Questions

What is an Omega bumper automatic?

It is Omega’s early self-winding family, calibres 330 to 355 in the GF 620 catalogue. The oscillating weight swings through part of a turn and bounces off a pair of banking stop springs (part 330.1415) instead of spinning all the way round, which is the bump you feel on the wrist.

Which bumper calibre is in my Omega?

Omega’s records tie each reference to its calibre: 64 references on ten calibres. A seconds hand from the centre means the 350 to 355 group; small seconds at six means the 330 to 344 group; a date window means the 353 or 355. The number on the movement settles it.

Did the Constellation have a bumper movement?

Yes. Omega’s records list eight early Constellations from 1952 to 1954 with the 352 or the 354, among them CK 2648, CK 2652, OT 2648, OT 2700, OT 14355, KO 2782, OT 2782 and OT 2799.

Do bumper movement parts interchange?

Many do, by part number. The winding stem 340.1106 is printed for all eleven 28.10 mm bumper calibres, from the 340 to the 355, and the oscillating-weight parts sit in the shared 330.14xx block. Buy by the Omega number, not the model name.

When did Omega make bumper automatics?

The bumper references in Omega’s records run from 1943 (OJ 2402) to 1958, with most from 1949 to 1954.

Sources: Omega’s vintage database for references, names, years and cases; Omega GF 620-1 for designations, sizes and part numbers. Watch Breaker is not affiliated with, endorsed by or connected to Omega SA or the Swatch Group. Omega, Seamaster and Constellation are trademarks of Omega SA.