The short answer to "is my IW371613 fake" is that this reference gets copied a lot, but mostly with poor results. The Portugieser Chronograph has a clean dial and a simple case, which is exactly what a replica workshop wants, because there is not much complication to hide. The good news is that the parts which are hard to copy are also the parts you can check yourself in about ten minutes with a loupe, a caliper, and a phone camera.
IW371613 sits in the 41mm steel Portugieser Chronograph family. If the watch in front of you is not 41mm across, not about 13mm thick, and does not have two subdials at 12 and 6 with no date window, the conversation is over.
What the real watch is
Steel case, 41mm, roughly 13.1mm tall, box-domed sapphire crystal, pump chronograph pushers, 3 bar water resistance. Dial with applied Arabic numerals and leaf hands. Two counters only: chronograph minutes at 12, running seconds at 6. No date. Inside sits the in-house calibre 69355, a column wheel chronograph at 4Hz with about 46 hours of reserve, visible through a sapphire caseback.
That spec sheet is your checklist. Keep it open while you look at the watch.
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Check one: case size and heft
Measure it. A caliper across the case at 3 and 9 should read 41.0mm, maybe 41.1. Thickness at the crystal edge lands near 13mm. Fakes tend to run 40mm or 42mm and a touch thicker, because the movement underneath is a Valjoux 7750 derivative or worse. Weight follows the size: a steel Portugieser on a strap sits around 80 to 90 grams. Something that feels light and hollow in the hand is a warning sign.
Check two: the dial
This is where most replicas fall apart, and it needs no tools to see.
- Subdials. Two, at 12 and 6. A date window at 3, a third counter, or stray text that should not be there means the watch is wrong.
- Numerals. Applied, polished, crisp edges, flat tops. Fakes use stamped numerals with soft corners and odd proportions, especially on the 4 and the 8.
- Printing. The minute track and the small IWC signature stay sharp under 10x magnification. On fakes the track looks fat and the text sits a hair off center.
- Hands. Leaf shaped, tapered, correctly curved. Look for burrs on the edges and lume fill that is uneven or on hands that should be plain.
- Subdial finish. Both counters carry fine concentric snailing. Fakes often use flat or coarsely grooved discs.
Check three: caseback and movement
The genuine IW371613 has a sapphire exhibition back. You should see a well-finished calibre 69355: stripes on the bridges, a signed rotor reading Probus Scafusia, blued screws, and a column wheel you can actually spot. Replicas either hide the movement behind a solid back or show a decorated 7750 with the wrong bridge layout. Look at the depth of the rotor engraving, the balance wheel position, and the finishing on the chronograph bridge. Engraving you can catch with a fingernail is a bad sign.
Then work the pushers. A column wheel chronograph starts and stops with a light, clean click. A 7750 clone feels mushy and the reset can stick.
Check four: papers, serial, price
The serial on the caseback should match the warranty card and the IWC registration record. Ask the seller for a clear photo of both, plus a shot of the movement. New retail on this reference runs around $8,000 to $8,700 depending on strap or bracelet. Used examples trade below that, but not into the floor. If the asking price is $2,000, you are not getting a bargain, you are getting a replica.
An IWC boutique or a watchmaker who services IWC can authenticate the watch during a service estimate. That estimate is the cheapest insurance in this hobby.
What replicas get wrong most often
- Crystal shape. Flat instead of box-domed, or a dome that sits too tall above the bezel.
- Crown. A soft, shallow logo, or a crown that is too small for the case.
- Strap. Embossed calf posing as alligator, with a scale pattern that repeats in an obvious way, and a stamped buckle instead of a milled one.
- Gaskets. The caseback says 3 bar, but the seals are missing or dry.
If you already own it and you are unsure
Get it in front of someone who services IWC. Ask for a movement photo and a written service estimate. Do not ship anything back to a seller before you have that in hand, and if you bought online, open the return claim while the window is still open. Waiting costs you the claim, not the seller.