The Royal Oak Selfwinding Chronograph 50th Anniversary in reference 26240ST.OO.1320ST.01 is a 41 mm stainless-steel flyback chronograph with a Bleu Nuit, Nuage 50 “Grande Tapisserie” dial, a steel bracelet, Calibre 4401 and a 70-hour power reserve. What marks it as an anniversary piece is the dedicated “50-years” oscillating weight, visible through the sapphire caseback. This article is a specification-and-design read based on Audemars Piguet’s published material and attributed press coverage. It is not a first-person wrist test.
What reference 26240ST.OO.1320ST.01 is
Audemars Piguet’s official product page identifies the reference as the 41 mm stainless-steel Royal Oak Selfwinding Chronograph in the 50th-anniversary series. The reference breaks down as a steel case and bracelet with a blue dial, and the “50” in the dial name signals the anniversary edition.
Official specifications
All figures below are Audemars Piguet’s published specifications from the current official product page (accessed 2026).
| Item | Specification |
|---|---|
| Reference | 26240ST.OO.1320ST.01 |
| Case | Stainless steel, 41 mm diameter, 12.4 mm thick |
| Water resistance | 50 m |
| Crystal and caseback | Glareproofed sapphire crystal; sapphire caseback; screw-locked crown |
| Dial | “Bleu nuit, nuage 50” with “Grande Tapisserie” pattern and matching counters |
| Hour markers and hands | White-gold applied hour markers; Royal Oak hands with luminescent coating |
| Bracelet | Stainless steel with AP folding clasp |
| Movement | Calibre 4401, selfwinding flyback chronograph; hours, minutes, small seconds, date |
| Movement details | 40 jewels; 70-hour power reserve; 4 Hz (28,800 vph) |
| Anniversary detail | Dedicated “50-years” oscillating weight, visible through the caseback |
Audemars Piguet’s US page showed $44,400 when it was captured in search results. That is a region-specific retail figure from the manufacturer’s site, not a transaction or secondary-market price. Check the live page before relying on it.
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- Sise: 10.5mmx1.5mmx1.0mm M:1.4mm
- Package Include: 4 pieces
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What changed in the 2022 Royal Oak line
This reference belongs to the 2022 design evolution of the Royal Oak. Audemars Piguet says the identifying codes stayed central: the tonneau-shaped case, the octagonal bezel and the eight visible hexagonal screws. The changes were ergonomic adaptations to case, bracelet and dial across new selfwinding and chronograph references in 34, 37, 38 and 41 mm.
The manufacturer describes the new finishing this way: “The case and bracelet encompass larger polished chamfers for a slenderer aesthetic offering stronger plays of light between the satin-brushed and polished surfaces.” That is Audemars Piguet’s own description, not an independent assessment. The brand also says the caseback is more integrated into the case for improved comfort.
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- Material: Stainless Steel
- LACAK Hexagon Watch Pusher Screwdriver compatible with Audemars Piguet Royal Oak 41mm Chronograph Watch Push Button
- Fit for Model Number: 26315ST.OO.1256ST.01; 26320OR.OO.D002CR.01; 26331OR.OO.D315CR.01; 26331ST.OO.1220ST.03; 26331ST.OO.1220ST.01...
- Quantity: 1 piece
- Note: This watch part is top-quality brand new aftermarket replacement product. Please do not confuse them with genuine part.
The anniversary rotor
Audemars Piguet states that the 37 mm and 41 mm selfwinding and selfwinding chronograph models in this evolution received a dedicated openworked 22-carat-gold oscillating weight with the “50-years” logo and the AP signature. For this reference, the official page lists the 50-years weight and the sapphire caseback that displays it. Because dial, metal and reference suffixes vary across the family, check the configuration of any other reference you are considering rather than assuming it matches.
Chronograph versus the simpler selfwinding models
The main differences in the evolved collection are these:
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- VERIFY YOUR WATCH MODEL & MEASURE THE CORRECT SIZE USING A RULER – Watch Parts Are Model and Size Specific. Please Verify Compatibility Before Purchasing.
- Compatibility & Size: Watch Band Bracelet, compatible with Audemars Piguet Royal Oak Offshore Safari Stainless/S, Royal Oak Offshore models.
- Ensure Perfect Fit: Verify the size, color, and model compatibility with your specific watch before purchasing to ensure a perfect fit and avoid returns or exchanges.
- Compatibility Check: Double-check your watch's requirements and compatibility details to ensure the product meets your needs. This will help you avoid any issues with returns or exchanges.
- Aftermarket Product: This is an aftermarket/generic made to original factory specs for a precise fit.
- Function and calibre: Audemars Piguet says the 41 mm chronograph models use Calibre 4401, a flyback chronograph. The 37 mm selfwinding models introduced Calibre 5900, a different movement that is not the one in this watch.
- Size: This reference is 41 mm and 12.4 mm thick. The line also offers 34, 37 and 38 mm cases, so the choice partly comes down to wrist and taste. No wrist-fit claims are made here, since none of the available sources measured them.
- Dial: The “Grande Tapisserie” pattern is shared across the family, but colour and material vary by reference suffix. Here it is Bleu Nuit, Nuage 50, with matching counters.
- Anniversary rotor: Both the 37 mm and 41 mm selfwinding and chronograph models carry the 50-years weight, so it does not separate this watch from its simpler siblings. The chronograph does add its own sub-dials and pushers to the dial.
Other hands-on coverage
Fratello Watches published a hands-on of the 41 mm Royal Oak Selfwinding Chronograph 50th Anniversary, and The 1916 Company ran a 2022 video review of this exact reference. Those are those publications’ own impressions, and their conclusions on wear and finish should be read there rather than assumed here.
Quick Recap
Best Value
- Wacth Band Screw Tube Replacement for the Audemars Piguet Royal Oak Offshore watch case which has 28mm straps.
- It fit all version of Royal Oak Offshore Chronograph including Safari, Alingi, Polaris, Barrichello, Orchard Road, Arnold , Montoya, Jay-Z, Volcano, Offshore Dual Time, Sincere, Rodeo Drive, Monte Napoleone, Worth Avenue, Tantalum, Royal Oak Offshore Scuba Wempe, Royal Oak Offshore Scuba La Boutique in All Versions.
- Size: 28mm
- Packing: 2 pcs tubes and 2 pcs screws
- Material: Stainless Steel
What to verify before buying
- The full reference number, including the suffixes, on the listing or paperwork.
- The current price on Audemars Piguet’s official page for your region; secondary-market values move and are not established by the sources used here.
- Whether the watch you are looking at has the 50-years rotor visible through the caseback, as the official specification describes.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
