The short answer: a fake Audemars Piguet Royal Oak Chronograph ref. 26331 is a counterfeit built to copy a 41 mm steel Royal Oak chronograph, and it usually gives itself away in three places. The case is the wrong size or too thick, the dial lacks true Grande Tapisserie texture, and the movement is a generic chronograph rather than an Audemars Piguet calibre 2385. Check those three in that order before you look at anything else.
What the Genuine 26331 Is
The 26331ST is a 41 mm stainless steel Royal Oak chronograph with an integrated bracelet, an octagonal bezel held by eight hex screws, and a three-register chronograph layout with a date display. Audemars Piguet builds it around calibre 2385, a 3 Hz movement with roughly 40 hours of power reserve. Water resistance is rated to 50 metres. Steel 26331 references sold in volume, so counterfeits exist for nearly every dial colour.
How to Check One
- Measure the case diameter across the bezel. Genuine is 41 mm. Most fakes land at 42 mm or larger because the donor case cannot be machined thinner.
- Measure case thickness. A genuine 26331 sits close to 11 mm. Counterfeits built on a Valjoux 7750 base often run 13 mm to 15 mm and ride high on the wrist.
- Turn the dial toward light. The Grande Tapisserie squares on a genuine dial are cut, with sharp edges and real depth. Printed or stamped squares look flat.
- Check the subdial spacing. The three registers should sit at 3, 6 and 9 with even gaps and printed numerals that do not crowd the date aperture.
- Press the chronograph pushers. Start, stop and reset should feel firm and identical. A mushy reset or a hand that does not snap back to zero points to a cheap module.
- Inspect the bracelet and clasp. Genuine links are held by screws, not friction pins, and the clasp stamping is deep and even.
- Read the case back engraving. Genuine engraving is cut deep with crisp edges. Laser etching looks grey and shallow.
- Listen to the movement and feel the winding. Calibre 2385 beats at 21,600 vibrations per hour, so a fast, buzzy rotor and a rough crown are warnings.
Common Tells on a Fake 26331
Beyond size and thickness, the most frequent failures are the bezel screws, often polished instead of brushed on their flat tops, and the dial text, which sits slightly high or low on the counterfeit dial. Date fonts on fakes are usually too bold. The bracelet taper is another giveaway. Genuine Royal Oak bracelets narrow steadily from the case to the clasp, while counterfeit bracelets stay wide and then drop sharply at the last link.
Before You Buy or Trade
Ask for a movement photo, a measured thickness, and a receipt from an authorised dealer. Price is the last filter, not the first. A 26331 offered far below current market is a fake or a stolen watch, and no photograph settles that question. Have any serious candidate opened and verified by a watchmaker who services Audemars Piguet.