In the replica Audemars Piguet market, "11 45100" is a caseback stamp that sellers quote as a factory or batch code. It is not an Audemars Piguet reference number. Real AP references use a different layout, such as 15500ST or 26240ST. The stamp on the back tells you which mold, movement, and production run a replica came from.
That detail matters because the same model ships from several workshops with the same outside look and different internals. One batch may hold a decorated Miyota 9015. Another may hold a clone caliber with copied bridges. The caseback code is one of the few clues you get without opening the case.
How Audemars Piguet reference codes work
Audemars Piguet stamps more than one set of numbers on a caseback, and each set does a separate job. A reference names the model. A serial names the single watch. Movement marks name the caliber inside.
- Reference number: five digits plus a metal suffix. 15500ST is a steel Royal Oak, 16202ST is the steel Jumbo, and the letters after the digits name the metal.
- Serial number: a longer string of digits, stamped on the back of modern pieces. It points to one watch, not to a model line.
- Caliber mark: the movement name, often written with a size figure in lignes and a number, such as 11 ½ lignes for a movement about 25.6 mm wide.
Those three numbers are different animals. Buyers mix them up, and that mix-up is how a stamp like 11 45100 gets treated as a model name.
Where a code like 11 45100 appears on a replica Audemars Piguet
Caseback
Replica AP casebacks carry a cluster of stamps. The reference line often copies a real model, while the extra numbers come from the mold itself. Some sellers add a code to flag the batch.
Check how deep the engraving sits, how the font reads at 3x zoom, and whether the letters follow the caseback ring. Shallow, blurry, or crooked stamps point to a cheap die.
Movement and rotor
Decorated movements add their own marks. A clone caliber copies the bridge shapes and the engraving of the original. A Miyota or ETA base keeps its own plate and a printed rotor.
Ask for a photo of the movement, not the caseback. The movement says more about the build than any number on the outside.
Clasp, crown, and mid-case
Stamps repeat on the clasp, the crown, and the case flank. A batch often gets the clasp right while the caseback font stays wrong. That gap is a useful tell when you compare two sellers side by side.
Do these codes identify a specific factory?
No public list maps a stamp like 11 45100 to a workshop. The trade groups replica AP watches under labels such as ZF, APSF, Noob, JF, KMF, and OMF, and those labels come from dealers, not from the metal.
Two sellers can offer the same watch under different code labels and ship identical product. Ask about the parts that decide quality instead: movement type, case width in millimeters, thickness, caseback shape, and bracelet taper.
What to check besides the code
- Case width and thickness against the real model. A Royal Oak 15500 measures 41 mm across and about 10.5 mm thick.
- Bezel screws. The slots should line up along the same axis around the octagon.
- Dial pattern. Tapisserie squares stay sharp near the center on a good dial and blur into mush on a weak one.
- Date window position and date font weight.
- Bracelet taper, plus link screws that sit flush with the surface.
- Movement finish. Geneva stripes should follow the curve of the plate, not run straight across it.
- Ask for the movement photo first.
- Get the thickness measured with calipers.
- Compare caseback engraving at zoom against a real reference.
- Compare the dial under raking light.
What a code like 11 45100 cannot tell you
A number on the back says nothing about water resistance, service life, or finish on the inside. Molds change without notice, and a code that looked clean last year may come from a new die this year.
Treat the stamp as one piece of evidence. Lean on photos, specs, and return terms far more.
FAQ
Is 11 45100 an Audemars Piguet caliber number?
AP does use lignes figures for movement sizes, and 11 ½ lignes fits several modern calibers. Public AP materials list calibers by name and number, and a string in this exact format does not come from those lists. Read it as a stamp from the caseback mold.
Do all replica AP watches carry the same caseback code?
No. Codes shift by batch, by model, and by mold revision. Two watches from one seller can carry different numbers a few months apart.
Should I pay extra for a specific code?
Pay for the movement, the case shape, and the dial. A seller who charges more for a stamp alone has nothing else to offer.
How do I compare two replica Audemars Piguet watches fast?
Line up four things: movement photo, measured thickness, caseback engraving, and dial pattern. Whichever watch wins three of the four is the one to buy.