The short answer
The 25721ST is the 1993 Royal Oak Offshore, the 42mm steel chronograph collectors call "The Beast." Replicas of it exist in several grades, and the honest version of the story is simple: none of them are 1:1 in the literal sense. The good ones land the case proportions, the Mega Tapisserie dial texture and the bracelet end links close enough that you would need to hold the watch in hand to catch the gaps. The bad ones miss thickness, dial depth and date font, and you can spot that from a phone photo.
So the useful question is not "is it fake or real." It is "which version is this, and what did they get wrong."
Why this reference is hard to copy
Emmanuel Gueit designed the Offshore around a case that did not exist before it: 42mm wide, about 14.5mm thick, with a rubber clad crown and pushers, a guarded crown assembly, and a bezel held by eight hexagonal screws. The dial uses AP's Mega Tapisserie pattern, a raised waffle grid stamped into a brass blank and finished by hand. Every one of those steps is a manufacturing problem. A factory that gets the case right often gets the dial wrong, and the other way around.
The original ran a Frédéric Piguet 1185 based caliber, the 2226/2840. That movement is thin, which is most of the reason the real watch wears the way it does. Replica makers do not have it. They use an Asian 7750 or a decorated clone, and that single fact drives nearly everything you can see on the wrist.
What a strong replica gets right
Case and bezel
Thickness lands near 14.5mm to 15mm, and the caseback curve matches the case instead of sitting flat like a lid. The bezel screws are hex and sit flush. They are not slotted, and they are not glued in crooked. The crown guards are cut, not cast, and the brushed sides run vertically with polished chamfers that break cleanly where the two finishes meet.
Dial
The tapisserie squares should have depth and a slight sheen when you tilt the watch, not a flat printed grid. Three registers, date at 3, applied AP logo at 12, and markers that sit at the right heights. The date font is thin with a flat top on the numeral one. Cheap builds use a fat generic date wheel, and it stands out immediately next to everything else on the dial.
Movement
You want a 7750 based automatic with a chronograph that starts, stops and resets cleanly. Ask how the seconds register is set up and whether the layout was modified to match the reference or dropped in as-is. On a lot of low end builds the running seconds hand sits where the donor movement put it instead of where the reference puts it. That is a tell you can confirm without opening the case.
Strap and bracelet
Rubber should be soft, sit flush between the lugs, and hold the right keeper shape. Steel bracelet end links should meet the case with no gap and no rattle. A bracelet that flexes side to side at the lugs is a giveaway that tolerances were not measured from a genuine sample.
Photo checks that catch most bad reps
- Look at the case profile from the side. Slab sided and flat usually means 2mm too thick.
- Ask for a close crop of the date window. Blurry print or a mismatched font ends the conversation.
- Count the bezel screws. Eight, hex, aligned with the caseback screws.
- Tilt the dial. Flat grid means a printed dial, not tapisserie.
- Request a video of the chronograph start, stop and reset.
Red flags in listings
"1:1 Swiss made" is a phrase, not a spec. Nobody is putting a Swiss chronograph movement in a 25721ST replica at a normal price. Listings that show only stock photos, no caseback, no movement shot and no date close up tend to hide the three things buyers actually care about. If the seller will not send a photo of the watch on a scale with the thickness visible, that is your answer, and it costs you nothing to move on.
What 1:1 means in practice
In the replica world, 1:1 means the case was measured from a genuine sample and the parts were made to those numbers. It does not mean the parts are interchangeable with genuine ones, and it does not mean a watchmaker could not tell in ten seconds with a loupe and a caseback tool. Treat the claim as a grade, not a guarantee.
Bottom line
The 25721ST is one of the hardest references to copy well, which makes it a good test of a seller. Get clear photos, ask about thickness, movement layout and date font, and compare what you receive against reference details rather than marketing copy. If the details hold up in a photo, the watch is worth a closer look. If the seller dodges the questions, walk.