Audemars Piguet Reference Number Guide
An AP reference identifies a model or configuration shared by multiple watches. It is not the individual case serial, movement number, calibre number or Royal Oak small number.
Decode the complete reference from left to right, but verify every unusual or modern compound code against the official product sheet rather than forcing it through an unofficial universal chart.
Reference, case number, movement number and calibre are not interchangeable
| Identifier | What it identifies | Is it unique to one watch? |
|---|---|---|
| Model/reference number | The model or exact configuration: case, decoration, bracelet or strap and dial. | No. Multiple watches can share it. |
| Big case number | One individual case recorded by AP; commonly called the serial in trade. | Yes. |
| Movement number | One individual movement engraved on a baseplate or bridge. | Yes. |
| Small Royal Oak number | A separate owner-facing sequence used on Royal Oak models, beginning with the 5402. | Individual within a model/material sequence, but not the big case serial. |
| Calibre number | A movement design or family, such as 4302 or 4401. | No. Many watches use the same calibre. |
Use the complete model reference as the exact product identity or MPN in catalog data. Keep individual case and movement numbers out of public structured data and public product imagery whenever possible.
Anatomy of a modern AP reference
Consider 15510ST.OO.1320ST.06, an official Royal Oak Selfwinding reference. AP’s published structure separates the root model, case material, decoration/setting position, bracelet or strap assembly and exact dial/configuration suffix.
| Segment | Example | Meaning |
|---|---|---|
| Root model | 15510 | The broad Royal Oak Selfwinding model family. |
| Case material | ST | Stainless steel. |
| Decoration/setting position | OO | Standard decoration in AP’s published reference structure. |
| Bracelet assembly | 1320ST | Royal Oak bracelet reference with steel material code. |
| Dial/configuration suffix | 06 | The exact variant within this model family; confirm it on the official product page. |
The root 15510ST is useful conversational shorthand but is not exact product identity. It does not specify every dial. A catalog title, SKU, MPN, guide card and canonical product page should use the full reference when available.
Common AP material codes
| Code | Material | Code | Material |
|---|---|---|---|
| ST | Stainless steel | OR | Pink gold |
| BA | Yellow gold | BC | White gold |
| PT | Platinum | TI | Titanium |
| CE | Black ceramic | CB | White ceramic |
| SA | Steel and yellow gold | IP | Titanium and platinum |
| OI | Pink gold and titanium | RO | Pink gold and ceramic |
| FO | Forged carbon and ceramic | SK | Steel and rubber |
AP’s historical code table is extensive and includes materials that appeared for a limited period. A compound code should be checked against the exact official reference. Do not guess from the first letter or assume every two-letter pair follows a simple metal formula.
ZZ appears in the decoration/setting position on factory gem-set references. It should be described as factory gemsetting context only after the exact AP product is verified; the presence of letters in a copied listing is not proof that stones or setting are factory original.
Bracelet, strap, clasp and dial segments
Modern references can encode a metal bracelet assembly or a flexible strap and buckle. In AP’s published structure, an A in the buckle position generally denotes a pin buckle and D a folding/deployant clasp. The following digits and letters can identify color, strap material and assembly.
The final two-digit suffix identifies a dial or configuration within the model family, but it is model-specific. For example, .06 on one root does not establish that .06 on every AP is the same color. Use the official page for the complete reference.
- Do not convert a root reference into an exact product without the suffix.
- Do not assume a strap reference can accept the bracelet from another suffix.
- Do not use a dial suffix as a universal color dictionary.
- Do not infer factory gemsetting from photos alone.
From four-digit models to exact modern configurations
AP introduced model numbers in 1951. Early references used four digits. Five-digit roots entered production around 1984–1985 and appeared in catalogues from 1986. AP renumbered some older models: the 5402 became 25402 and the 8638 became 78638 in the later system.
From the early 2000s, references progressively expanded with case material, decoration, buckle, bracelet or strap, material and dial information. Historical references do not always contain every modern segment, and the model number itself is only rarely engraved on older watches.
Decode the structure without over-decoding
| Reference | What can be stated safely | What still requires verification |
|---|---|---|
| 15510ST.OO.1320ST.06 | 15510 root; steel case; standard decoration; steel Royal Oak bracelet; exact .06 configuration. | Confirm the dial description and current product facts on AP’s official page. |
| 15551OR.ZZ.1356OR.05 | 15551 root; pink-gold case; factory gemsetting context; pink-gold bracelet; exact .05 configuration. | Confirm stones, dial and complete factory configuration on the official product record. |
| 26240OR.OO.D404CR.02 | 26240 root; pink-gold case; standard decoration; deployant/strap assembly; exact .02 configuration. | Confirm strap color/material and dial from the exact product sheet. |
| 26420CE.OO.A043VE.01 | 26420 root; black-ceramic case; standard decoration; pin-buckle/strap assembly; exact .01 configuration. | Confirm the complete strap and dial execution officially. |
| 26331IP.OO.1220IP.01 | 26331 root; titanium/platinum case code; standard decoration; matching integrated bracelet assembly; exact .01 configuration. | Confirm the exact material distribution and dial on the official reference. |
A product handle or title can become stale when a listing is repurposed. The exact SKU/reference and live product content must agree. A URL whose old handle contains “15500” but whose page now describes a 15510 is a 15510 product, not evidence of a live 15500.
Reference verification workflow
- Obtain the complete reference from the watch, papers and seller record.
- Compare it with AP’s official product or archival material.
- Confirm case material, dial, bracelet or strap, clasp and movement are coherent.
- Inspect for service replacements, aftermarket components or title/reference mismatch.
- Reconcile private case and movement numbers with documentation without publishing them.
- Use qualified physical authentication; do not rely on an online code decoder.
Then use the AP serial and date guide to understand the separate individual-number systems and their limits.
References that illustrate AP number structure
Use these live product records to compare exact references after deciding which collection, size, movement, material and condition profile fits your priorities.
Audemars Piguet reference-number FAQs
Is an AP reference number unique to one watch?
No. A reference identifies a model or exact configuration shared by multiple watches. The individual case and movement numbers are separate.
What do ST, OR, BA, BC, TI and CE mean?
They are case-material codes: steel, pink gold, yellow gold, white gold, titanium and black ceramic respectively.
What does the final number in an AP reference mean?
It identifies an exact dial or configuration within that model family. The same suffix is not a universal color code across all AP roots.
Is OO part of the root reference?
No. In AP’s published structure, OO occupies the decoration/setting segment after the root and case-material code.
Can a reference number prove an AP is authentic?
No. A correct reference is one consistency check. Authentication requires examination of the watch, components, provenance and, where needed, AP expertise.
Why must buyers compare the entire reference?
The root alone may omit dial, bracelet or strap, clasp, material and gemsetting details that materially change identity and value.
Sources and methodology
AP Chronicles: Audemars Piguet watch numbering · AP Royal Oak 15510ST.OO.1320ST.06
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.