A fake Audemars Piguet Royal Oak 15202ST fails on three points: case thickness, movement beat rate, and dial texture. The genuine watch is 39 mm wide and 8.1 mm thick in steel. It runs caliber 2121 at 19,800 vibrations per hour. A replica built on a Miyota 9015 or a Chinese clone cannot match those numbers without a false case back or a shaved dial. Measure the case flank with calipers before you look at anything else.
What the 15202ST is
The 15202ST.OO.1240ST.01 is a stainless steel Royal Oak. Audemars Piguet introduced the Royal Oak in 1972 as the 5402ST, designed by Gerald Genta. The 15202 kept the 39 mm case, the octagonal bezel with eight hexagonal screws, and the integrated bracelet. The dial carries the Petite Tapisserie pattern, a grid of small pyramids. There is a date at 3 o'clock. There is no seconds hand. Water resistance is 50 m. The watch uses caliber 2121, a 3.05 mm self-winding movement based on the Jaeger-LeCoultre 920. It has 36 jewels and a 40 hour power reserve. Audemars Piguet discontinued the 15202 in 2022 and replaced it with the 16202, which uses caliber 7121.
Check 1: Case thickness
Genuine: 8.1 mm. Most replicas: 9.5 mm to 11 mm. The gap comes from the movement. A Miyota 9015 measures 3.9 mm. Caliber 2121 measures 3.05 mm. Add the case back, dial, and hands, and the difference shows at the flank. Measure at the side of the case, near the 9 o'clock position, away from the crystal. Do not measure across the bezel and crystal, which adds about 1 mm on any watch.
Check 2: Movement
Look through the display back. Caliber 2121 has a decorated rotor with an engraved AP signature, Geneva stripes on the bridges, and blued screws. Fakes show a Miyota rotor, a stamped plate, or a printed logo. Beat rate is the harder test. Caliber 2121 runs at 2.75 Hz, 19,800 vph. Most clone movements run at 4 Hz, 28,800 vph. You cannot read the beat rate on a 15202 because the dial has no seconds hand. Use a timegrapher or a slow-motion video of the balance wheel through the case back.
Check 3: Dial and bezel
The Petite Tapisserie pyramids are cut, not molded. Under a loupe the pyramid tops are flat and the side walls are sharp. On most fakes the pattern is shallow and the tops are rounded. The bezel holds eight functional hex screws. Screw slots on the genuine watch do not line up in one direction. Many fakes show all eight slots aligned, because they are decoration and not screws. The date sits in a window with no frame, and the numerals use the AP font. Fakes use a wider window or a different numeral shape.
Check 4: Bracelet and clasp
The 15202 bracelet is thinner than the 15400 bracelet and tapers toward the clasp. Link edges are beveled and polished on the outer faces, brushed on top. The clasp is a folding type with the AP name. Replica bracelets show sharp link edges, uneven brushing, and a clasp with a shallow stamp. Flex the bracelet. Genuine links move without rattle.
Case back and numbers
The case back carries the reference 15202ST.OO.1240ST.01 and a serial number. Engraving is deep and even. Replicas repeat one reference and one serial across a batch. Ask for a photo of the case back and compare the digits to the seller's other listings. Matching numbers on two watches is a stop sign. An Audemars Piguet service center can confirm a serial.
What photos cannot show
Lighting flattens the tapisserie. A phone photo at 12 inches hides the pyramid height. Thinness does not read in a wrist shot. Ask for a caliper photo at the case flank and a macro shot of the dial at 3 o'clock. If the seller refuses, stop. At this price level, a service center inspection is the test that ends the question.