Short answer

Reference 16402 does not appear in the Audemars Piguet Royal Oak catalog. Time-and-date Royal Oaks carry numbers such as 16202, 15202, 15500, and 15400. When a listing says 16402, either the seller mistyped the reference or the number was invented for the ad. Verify the reference first, then work through the physical checks below.

Prerequisites

  • A 10x jeweler's loupe
  • Digital calipers
  • A gram scale
  • A bright, directed light
  • Reference photos of the exact Royal Oak model
  • Access to a watchmaker who can open the caseback

Step-by-step verification

  1. Open the Audemars Piguet site or an official catalog and search the reference number. If 16402 is absent, treat the listing as unverified.
  2. Ask the seller for a close photo of the reference engraving on the caseback. A seller who cannot supply one is a warning sign.
  3. Measure the case diameter with calipers. Royal Oak time-and-date cases come in 37 mm, 39 mm, and 41 mm depending on reference. A 41 mm watch labeled as a 39 mm reference is wrong.
  4. Measure the case thickness. A Royal Oak Jumbo sits near 8 mm, while a 41 mm time-and-date runs above 10 mm. Compare your reading to the published spec for that exact reference.
  5. Examine the dial grid under the loupe. Grande Tapisserie squares should sit at even spacing with sharp, straight edges and clean corners.
  6. Check the dial printing. The AUDEMARS PIGUET signature and the AP monogram should be crisp, centered, and thin. Thick or smeared text is a common replica fault.
  7. Inspect the date window. The aperture should have a clean frame and even border, and the date should sit level and centered.
  8. Study the hands. Royal Oak hands have flat, polished surfaces with sharp edges and a clean bevel along the sides.
  9. Run a finger along the bracelet links. The links should move without binding, and each link should carry a straight polished bevel that catches light in one continuous line.
  10. Check the case finishing under angled light. Brushed surfaces should be uniform, and the polished bevels should form a straight, unbroken edge along the case flank.
  11. Turn the crown. A genuine screw-down crown threads without grit and seats flush against the case.
  12. Weigh the watch. A steel Royal Oak on a full bracelet has real mass. Compare your reading to the listed weight for that reference.
  13. Have a watchmaker open the caseback. On display-back models, check the rotor, engraving depth, and movement finishing. On solid-back models, confirm the engraved reference and serial.

Legal note for US buyers

Counterfeit watches are illegal to import and sell in the United States. CBP can seize a shipment at the border, and sellers face civil and criminal penalties under trademark law. The terms replica and first copy are marketing labels. No first copy watch is manufactured by Audemars Piguet, and no authorized dealer will service one.

What to do with the result

If two or more checks fail, walk away from the deal. If the watch is genuine, request a written service history and a watchmaker's inspection before money changes hands.