If you searched this reference because someone put a watch in front of you, here is the short answer. The Audemars Piguet Royal Oak Offshore ref. 25721ST is a 1993 steel chronograph nicknamed "The Beast," and a real one now trades well into six figures. Copies show their seams fast. Bezel screw slots, dial depth, case thickness, and the movement are the four places a fake gives itself away, and you can usually find all four in under a minute.

What the 25721ST actually is

Audemars Piguet launched the Offshore in 1993 as a bigger, heavier, more aggressive reading of the Royal Oak. Reference 25721ST was the original steel model. The case measures 42mm across and about 15mm thick, which was enormous for a dress-adjacent brand at the time. The crown and both chronograph pushers are coated in rubber. The dial uses the Mega Tapisserie pattern, a grid of raised squares that catches light from the side. Subdials sit at 12, 6, and 9, with the running seconds down at 9. The date window is at 3. Inside is the calibre 2226/2840, a Jaeger-LeCoultre base carrying a Dubois-Depraz chronograph module.

That layout matters. Anyone selling a "25721ST" with a different subdial arrangement is selling a watch that never existed.

The tells, in the order I check them

Bezel screws

Eight hexagonal screws run around the octagonal bezel. On genuine pieces they are functional hardware that threads into the case, and the slot orientation is deliberate rather than random. Fakes often use decorative caps that sit on top of the bezel, or slots that wander in every direction. Run a fingertip across them. Anything that feels like a sticker or sits proud of the surface is wrong.

Dial depth and printing

The Mega Tapisserie grid is machined, not printed. Tilt the watch and the squares throw real shadows with beveled edges. Copies tend to be flat, shallow, or slightly soft at the corners. Check the "Audemars Piguet" signature under magnification. Real printing is crisp with no bleed, and the date font is thin and correct for the era. Look at the subdial rings too. Snailed finishing on a fake usually looks like a flat dark circle.

Case, crown, and back

The rubber on the crown and pushers should feel like dense rubber, not hard plastic. Caseback engraving on a real one is deep and sharp, with reference and serial numbers that match the paperwork and any service record. The bracelet tapers, has polished bevels on brushed links, and carries proper clasp engraving. Weight is a decent gut check. A 42mm steel Offshore has real heft in the hand, so a watch that feels hollow or light is a problem.

Movement

Fakes in this reference almost always run an Asian 7750 derivative or a quartz movement. Both show up in the same ways: the case runs thicker than it should, the chronograph pushers feel vague or grind, and the subdial functions do not match the real layout. If the seller will not open the back, that is your answer.

Price and paperwork reality

Original 25721ST examples have climbed hard at auction over the past decade. A complete set with box and papers is a five or six figure watch. When a listing lands at a few hundred dollars, or a "Swiss made" copy is pitched as a 1:1 replica, the price is the authentication. Nobody sells a real Offshore cheap.

There is a legal side too. Trafficking in counterfeit watches is a criminal offense in the United States, and Customs seizes replica shipments on arrival. A copy also cannot be serviced by the brand, cannot be insured properly, and has no resale value beyond whatever the next buyer will pay for a known fake.

If you want the Offshore look

Buy the real thing or buy a different watch. If budget rules out the 25721ST, look at a legitimately made steel chronograph with a similar wrist presence from a brand that will service it. That is a watch you can wear hard, hand down, and sell later without explaining yourself. Chasing a fake version of a 1993 icon means paying real money for something that fails the first screwdriver test.