Short answer
Ref 5402ST is the first Royal Oak. Audemars Piguet launched it in 1972. Production ran through the 1970s and into the early 1980s. No 5402 has left the factory since. Any watch sold as a new 5402 is not genuine. Most fakes tied to this reference are vintage cases with replacement dials, modern Royal Oak cases with a 5402 dial, or full counterfeits built on an ETA or Chinese movement. Case thickness, dial grid and caliber are the three fastest checks.
What the real 5402 is
- Reference 5402ST. Steel. 39 mm across. About 7.5 mm thick. Listed specs vary by source.
- Caliber 2121, an automatic movement built on the Jaeger-LeCoultre 920. Date at 3 o'clock.
- Bezel held by eight hexagonal screws.
- Dial with the Petite Tapisserie grid. The AP monogram sits at 12. The word Automatic sits below center.
- Series letters A, B, C and D. A-series came first.
Audemars Piguet does not publish production totals for the 5402. Figures cited by auction houses and collectors sit in the low thousands for steel. Treat exact counts as unknown.
Case and thickness
Measure the case with a caliper, crystal excluded. A genuine 5402 measures about 7.5 mm. Replicas built on ETA 2892, Miyota 9015 or Chinese automatic movements run 9 mm to 11 mm. Look at the case flank. On the real watch the flank is thin and the bezel edge sits close to the midcase. On fakes the flank is taller because the movement needs the room. Lugs taper from a wide top to a narrow tip. Many fake lugs stay wide and flat at the tip.
Dial
Petite Tapisserie squares are small and raised, with a matte finish on the top face. Replica dials use wider squares, shallow stamping and glossier paint. Run a finger across the grid. Real squares have edges. The printed name on the dial is thin and even. Fake printing is heavier and sits lower on the dial. The date window is small. Its frame is a thin printed border on most series. Fake date wheels use a different font and a taller aperture.
Movement
Caliber 2121 is 3.05 mm thick. Bridge shapes and finishing are specific: Geneva stripes on the bridges, a signed rotor, and a thin automatic winding module. A counterfeit with an ETA base shows different bridge geometry and a rotor that fills more of the caseback. A Chinese clone of the 2121 exists and copies the layout. The finish on clones is coarser. Screw heads are undomed. Jewel settings are pressed, not set in chatons. Have a watchmaker who services Audemars Piguet open the case.
Caseback and numbers
The caseback carries the reference and a case number. Genuine engraving is cut into the metal with even depth and thin strokes. Fakes use laser engraving, which leaves uniform depth and slightly rounded edges. Compare the case number against auction archives for A, B, C and D series watches. Numbers in the wrong range for the dial type point to a marriage of parts.
Price and market
Genuine 5402ST examples sell at auction in the high five figures to low six figures USD. A-series watches with box and papers go higher. A listing at $500 to $2,000 is not a 5402. Listings that show a new watch, factory stickers or a modern box are not 5402 watches either.
Why this reference gets faked less
Replica makers put most of their output into modern references: 15202, 16202, 15500. The 5402 is harder to copy because the thin movement drives the whole case design. Fewer full fakes exist. The larger problem is Franken watches: a genuine movement in a fake case, or a genuine case with a redial. Both pass a photo check and fail a hands-on check.
Checklist before you buy
- Measure case thickness with the crystal excluded.
- Count the Tapisserie squares and check the grid pattern.
- Check date font and aperture shape.
- Inspect the eight bezel screws for slot depth, threading and alignment.
- Compare caseback engraving font and depth to a known watch.
- Check movement bridges, rotor signature and finishing.
- Compare the case number to auction records for the series.
- Get a written opinion from a watchmaker who services Audemars Piguet.
Documentation matters less than the watch. Papers can be printed. A service record from an authorized center carries more weight than a box.