The 26403 is a 42mm Royal Oak Offshore chronograph, and the fakes sold under that reference are almost always built on an Asian Valjoux 7750 base with a decorative plate bolted over the movement. From three feet away, a good one reads correctly on the wrist. In the hand it does not. Three things give a replica away: case thickness, dial texture, and the movement underneath. Everything else, from the bezel screws to the strap, is a variation on those same problems.

What the real reference is

The 26403 sits in the 42mm branch of the Offshore chronograph family. That means an octagonal bezel held by eight hexagonal screws, a case roughly 42mm across and about 14.5mm thick, and a Mega Tapisserie dial with a raised waffle grid stamped into the surface. Inside is caliber 3126/3840, the 3120 automatic base with a chronograph module stacked on top. Subdials sit at 12, 6, and 9, with the date at 3. Bezel material and dial color change from one variant to the next, so pull up photos of your exact number before you compare anything.

Case, bezel, and the eight screws

On the genuine watch, the bezel screws are hexagonal, drop into countersunk recesses, and get their slot orientation set during assembly. They are not identical on every piece, but they are not random either. Replica bezels often use flat-head screws, slightly wrong head sizes, or slots cut too deep. Run a fingernail across one. A real screw sits flush or barely proud inside a clean chamfer.

Then look at the profile. An Offshore chronograph is a thick watch, but a 7750 build with a module plate often runs a millimeter or two over. The lugs look slab-sided instead of having brushed top surfaces that break into polished bevels. The crown and pushers should be rubber-coated, and the crown should screw down against a rubber gasket with a firm, short travel.

Dial and subdials

The Mega Tapisserie grid is the fastest visual tell. On a real dial the squares are cut with sharp edges, and as you tilt the watch the tops catch light unevenly across the surface. The printing on the subdial rings is crisp with no bleed at the edges. Replicas tend to have a softer, shallower grid that looks molded rather than stamped, subdial rings that are too glossy, and a date font a hair too wide. Hand stack height matters too. Genuine hands sit close to the dial; fakes sit high because the 7750 sits deeper in the case.

The movement is the dividing line

This is where a replica stops being convincing. The 3126/3840 has hand-applied finishing: polished bevels on the bridge edges, Geneva stripes, and a decorated rotor. A 7750 has industrial finishing with a printed rotor plate glued on top.

One field test works every time. Pull the crown out to the time-setting position and watch the running seconds subdial at 9. The genuine 3120 base hacks, so the seconds stop. The ETA 7750 family does not hack, so the seconds keep moving. If the watch keeps ticking while you set the time, you are looking at a 7750-based fake.

Caseback, serials, and engraving

Whether your reference has a display back or a solid engraved caseback depends on the variant, so check the exact number first. With a display back, you see the movement and the finishing question answers itself. With a solid back, look at the engraving. Genuine AP stamping is deep and crisp, with a slightly matte floor inside each letter. Fakes are laser-etched, shallow, and too even. Serials are unique per watch and can be verified through the brand, which is why a seller who refuses to show the number is telling you something.

Strap, clasp, and feel

A steel 42mm Offshore chronograph has real presence on the wrist. Replicas usually get the weight close, but the details slip. Stitching on a genuine rubber or leather strap is even and tight to the lug line. Clasp engraving is sharp. The bezel gasket seats without a gap. None of these are hard to check, and all of them are commonly wrong.

Price, resale, and the law

A genuine 26403 trades in the five-figure range on the secondary market depending on condition and completeness. A replica costs a few hundred dollars and holds no value, cannot be serviced at a brand service center, and uses parts matched to a 7750. Counterfeit watches are also illegal to import into the United States and illegal to sell as genuine, and shipments get seized regularly.

Quick checklist before you buy

• Measure the case thickness. Anything over spec is a warning.
• Pull the crown and check whether the seconds hand hacks.
• Tilt the dial and look for sharp, light-catching grid edges.
• Inspect the bezel screws for countersinking and head shape.
• Study the caseback engraving depth and the serial font.
• Ask for the exact reference, then compare against the brand's own spec sheet.

The plain version: a high-end replica of the 26403 can pass at a dinner table. It will not pass a watchmaker, a loupe, or a resale counter. Buy it as a look, and never let anyone sell it as the real thing.