Audemars Piguet Royal Oak Chronograph 26331 vs. 26240
The 26331 and 26240 are both 41 mm Royal Oak Chronograph generations, but they make different priorities. The 26331 is thinner and uses Calibre 2385; the 26240 is thicker and introduces AP’s integrated flyback Calibre 4401.
Compare the complete reference and individual watch. Steel, gold, titanium/platinum and strap variants can differ substantially from the standard examples used for the specification table.
26331 and 26240 specifications at a glance
| Specification | Royal Oak Chronograph 26331ST | Royal Oak Chronograph 26240ST |
|---|---|---|
| Case diameter | 41 mm. | 41 mm. |
| Stated thickness | 11 mm. | 12.4 mm. |
| Stated water resistance | 50 m on the referenced steel model. | 50 m on the referenced steel model. |
| Movement | Selfwinding Calibre 2385. | Selfwinding integrated flyback Calibre 4401. |
| Stated power reserve | 40 hours. | 70 hours. |
| Flyback function | No. | Yes. |
| Movement display | Movement is not presented through the same modern sapphire-back architecture. | Calibre 4401 is visible through a sapphire caseback. |
The 26240’s movement is the larger technical change; the 26331’s thinner profile and particular dial executions remain meaningful counterweights.
Traditional chronograph generation or integrated flyback
Calibre 2385 is an established automatic chronograph architecture used in the 26331 generation. It provides conventional start, stop and reset operation in a relatively thin Royal Oak Chronograph case.
Calibre 4401 is AP’s integrated automatic flyback chronograph. “Integrated” means the chronograph is designed into the movement rather than added as a separate module; “flyback” permits reset and restart with one pusher sequence while timing. The visible movement and longer stated reserve create a different technical proposition.
Those advantages do not make Calibre 2385 defective or irrelevant. Buyers should weigh service history, desired case thickness, dial preference and purchase price alongside movement architecture.
How 11 mm and 12.4 mm wear
Both references carry a broad 41 mm Royal Oak footprint, but 1.4 mm of additional stated thickness changes side profile and visual mass. The 26240 is not an Offshore, yet it has a more substantial presence than the 26331.
Compare side photographs and wrist video with the bracelet fitted correctly. A buyer who values thinness under a cuff may prefer the 26331; a buyer who prioritizes modern movement architecture may accept the 26240’s height.
Dial layout, caseback and generation character
Chronograph subdial scale, date placement, logo treatment, hand proportions and exact color determine much of the visual decision. Compare the complete suffix; a two-tone “panda” execution, blue dial and precious-metal variant do not share one market profile.
The 26240 adds the experience of viewing Calibre 4401 through the caseback. The 26331’s appeal is concentrated more heavily on the dial, case proportion and the specific discontinued execution. Neither should be described solely by movement.
How to inspect an AP chronograph
- Confirm the exact reference, movement, dial and material.
- Start, stop and reset the chronograph while observing hand alignment and pusher feel.
- On a 26240, test flyback operation appropriately.
- Inspect pushers, crown, bezel, case bevels, bracelet and clasp for impact or refinishing.
- Ask about service history, replacement components and current water-resistance testing.
- Confirm all links, box, papers and accessories without treating them as authentication.
A malfunctioning chronograph or uncertain service history can overwhelm a seemingly favorable purchase-price difference.
Choose by movement, profile and exact dial
Choose 26331 when
You prefer its thinner case, exact discontinued dial or price and have verified movement operation, condition and service.
Choose 26240 when
You want the integrated flyback Calibre 4401, sapphire movement view, longer stated reserve and later exterior evolution.
Pause when
The chronograph has not been function-tested, reset alignment is unclear, polishing has softened the case or service provenance is missing.
26331 and 26240 Royal Oak Chronographs
Use these live product records to compare exact references after deciding which collection, size, movement, material and condition profile fits your priorities.
Royal Oak Chronograph 26331 vs. 26240 FAQs
Are the 26331 and 26240 the same size?
Representative standard steel references are both 41 mm, but AP lists the 26331ST at 11 mm thick and the 26240ST at 12.4 mm.
Which reference has a flyback chronograph?
The 26240 uses integrated flyback Calibre 4401. The 26331 uses Calibre 2385 without flyback operation.
Why is the 26240 thicker?
Its modern Calibre 4401 architecture and case construction create a thicker 12.4 mm profile than the 11 mm 26331ST.
Can you see the movement in both references?
The 26240 presents Calibre 4401 through a sapphire caseback. The 26331 is not built around that same open caseback presentation.
Is the 26331 obsolete?
No. It is discontinued, but its thinner case, dials and generation-specific character can remain highly desirable.
What should be tested before buying an AP chronograph?
Test start, stop and reset; flyback where applicable; hand alignment; pushers and crown. Review service history, case geometry, bracelet, dial and replacement parts.
Sources and methodology
AP Royal Oak 26331ST · AP Royal Oak 26240ST · AP Royal Oak design evolution
Technical specifications and historical claims are checked against Audemars Piguet and AP Chronicles. Current price, imagery and availability are drawn from Superlative Watch Co.’s live Shopify product records.
Editorial review: July 27, 2026. Superlative Watch Co. is an independent luxury-watch dealer and is not affiliated with or authorized by Audemars Piguet. Product availability, pricing and specifications can change. Brand names and trademarks belong to their respective owners.