The Audemars Piguet Royal Oak 5402ST has a solid caseback, a 39 mm steel case, and two hands. A counterfeit shows a display back, a case over 9 mm thick, or a center seconds hand. No genuine 5402ST has those features.
What the reference is
Audemars Piguet launched the Royal Oak in 1972. Gérald Genta drew the design. The first model is the 5402ST. It came in four production batches: A, B, C, and D. A-series watches date to 1972 and 1973. Steel production stopped in 1977. Auction records put total steel output near 2,000 pieces. Audemars Piguet has not published a full number.
Case and thickness
Measure the case with a caliper. A 5402ST reads 7.2 mm to 7.6 mm at the center. Copies read 9 mm and higher. Look at the bezel edge. Genuine cases get an angled cut after finishing. Fakes show a rounded edge and a wide polished band. The eight bezel screws sit in slots cut into the case side. Slot angles should match the design of the same series.
Dial
The 5402ST carries a Petite Tapisserie dial. Stern cut the blanks on a pantograph machine. The grid is stamped into metal, so each square has a raised wall and a flat top. Fakes print the grid in ink. Under a loupe the fake surface stays flat. One genuine square measures under 1 mm across. Copies often use a coarse grid near 1 mm or a Grande Tapisserie pattern from a later reference. Logo text and its position changed from the A series to the D series. Compare a candidate against documented examples from the same batch.
Hands and date
The 5402ST has an hour hand, a minute hand, and a date. There is no seconds hand. A watch with a center seconds hand is not a 5402ST. The date sits at 3 o'clock in a beveled aperture. Genuine date wheels use a thin numeral font. Fake wheels use a bold font and a flat aperture.
Caseback and movement
The caseback is solid. It carries the reference number, the case serial, and the Royal Oak name in an engraved ring. A display back on a claimed 5402ST is a fake. The caliber 2121 is the decisive test. The 2121 comes from the Jaeger-LeCoultre 920 base. It has 36 jewels and runs at 19,800 vibrations per hour. Many rotors are 21k gold and carry the AP monogram. Counterfeit movements show stamped bridges, a plated rotor, and fewer jewels. A watchmaker can count jewels and check the balance in minutes. Serial records are held by Audemars Piguet. The company issues extracts from its archives for a fee.
Bracelet
The bracelet is integrated with the case and tapers toward the clasp. Link height drops along the run. Copy bracelets keep one link height from end to end. The clasp stamp varies by year. Match it to the case serial range before you buy.
Checks that need a watchmaker
- Jewel count and balance type on the caliber 2121.
- Case serial against the Audemars Piguet archive.
- Dial removal to confirm the grid is stamped, not printed.
- Case thickness with a caliper at the center.
Limits
Photos cannot confirm jewel count, serial, or dial construction. Records for the 5402ST are incomplete, and output figures come from auction research, not from the maker. A 5402ST with a replaced dial or a later service caseback is not a fake, but it sells at a lower price. Work with a watchmaker who has handled the reference.
Importing a counterfeit watch into the United States violates 19 U.S.C. 1526. Customs can seize the item and assess a penalty.