Quick answer

Reference 26403 is not one watch. The number covers a group of Audemars Piguet Royal Oak Offshore chronographs, and case metal, dial color, and strap change from variant to variant. Replica versions sell for about $250 to $700. Four checks decide quality: case size and thickness, dial texture, subdial layout, and the movement that drives the hands.

What the 26403 number covers

The Royal Oak Offshore came out in 1993. Designer Emmanuel Gueit drew it as a bigger, thicker take on the 1972 Royal Oak designed by Gerald Genta. The Offshore case is 42mm or 44mm on most chronograph references.

Audemars Piguet does not publish one single spec sheet for every 26403 suffix. Dial color, case metal, and strap differ across the range. Confirm the exact variant first, then compare a replica against photos of that variant.

Case and bezel checks

Count the screws in the bezel. A Royal Oak bezel holds 8 screws in a ring around an octagonal shape. Low grade replicas print flat screw heads. Better grades machine real hex sockets.

Measure thickness. A chronograph Offshore case runs about 14mm to 15mm. A case near 11mm holds a three hand movement, not a chronograph.

Check the crown and pushers. Many Offshore references use a screw down crown and threaded pusher guards. Pushers that sit below the case line or wobble point to a cheap build.

Dial and hands

The Offshore dial carries a tapisserie pattern, a raised grid of small squares. Genuine grids are cut and the square edges are sharp. Replica dials in the $250 to $400 band show shallow squares and soft edges.

Look at the subdials. The chronograph layout puts a 30 minute counter at 12, a 12 hour counter at 6, and running seconds at 9. The date window sits at 3. That layout matches the Valjoux 7750 family, which most replicas use.

Check hand finish. Genuine hands are faceted with polished bevels. Replicas show brushed or painted hands with rounded edges.

Movement

Two movements show up in 26403 replicas. The first is an Asian 7750, an automatic chronograph with a 12-6-9 subdial layout and 28,800 vibrations per hour. The second is a decorated clone that copies the AP calibre 3126/3840, including rotor engraving. Genuine 3126/3840 movements carry 59 jewels and about 50 hours of power reserve.

Test the chronograph. Start, stop, and reset the sweep hand 10 times. A healthy 7750 returns to 12 with no creep. A worn movement stops 1mm to 3mm off center.

Caseback, bracelet, and weight

Caseback engraving on a genuine AP watch is deep and sharp. Replica engraving is shallow and often off center.

Bracelet links on the Royal Oak use two screws per link, one per side. Count them. Genuine bracelets use flat head screws that take a 1.4mm to 1.6mm driver. Some replicas use pins or glue.

Steel Offshore bracelet versions feel heavy in hand, past 180g. Rubber strap versions sit near 120g to 150g. A steel bracelet watch near 130g is hollow inside.

What to verify before you buy

• Ask for the case diameter and thickness in millimeters.
• Ask which movement is inside and whether the chronograph returns to 12.
• Ask for caseback photos under direct light.
• Ask about the crystal: sapphire with anti reflective coating, or mineral glass.
• Confirm the return window and shipping terms.