Quick answer
An IW371628 is a stainless steel IWC Portugieser Chronograph. A genuine one has a 41 mm case, caliber 69355 inside, and a case back engraved with the reference number and a serial number that matches IWC records. A fake fails one of those points. The tells that show up most: laser-printed text on the case back, a generic automatic or quartz movement behind a display back, dial printing with the wrong font weight, and a price under $2,000.
What the reference covers
IWC builds the Portugieser Chronograph across several references in the 3716 family. The case measures 41 mm across and 13.1 mm thick. Water resistance is 30 m. The crystal is sapphire with antireflective coating on both faces. The movement is caliber 69355, an automatic chronograph with a column wheel and a 46-hour power reserve. Dial color, strap, and metal vary by reference. IWC publishes the exact configuration for each number on its own site. Confirm the IW371628 variant there before you compare anything else.
Checks in order
- Case back. Genuine engraving is deep with sharp edges. Fake text is shallow, sandblasted, or printed. Read the reference and serial under a loupe at 10x.
- Movement. Caliber 69355 shows Geneva stripes, blued screws, and a skeletonized rotor with the IWC medallion. Copies show unfinished bridges, a plastic movement ring, and Phillips screws.
- Dial. Subdial rings sit below the dial surface on the genuine watch. Printing holds a clean edge at 10x. Fake dials show fuzzy text and subdial hands that do not line up with the marks.
- Crystal. Sapphire shows a faint blue tint at an angle and no distortion at the rim. Mineral glass bends the dial edge and scratches with a steel pin.
- Weight. IWC publishes no weight figure. Compare the watch in hand against a known genuine example, not against a number from a listing.
- Strap and clasp. Genuine alligator straps carry a stamped IWC mark on the lining. The folding clasp closes with a firm click and the finish matches the case.
- Papers. A full set has a warranty card with the reference, the serial, and a dealer stamp. Ask an IWC service center to confirm the serial.
Price signals
Genuine IW371628 watches trade in the high four figures in US dollars on the secondary market. A seller who asks $300 to $1,500 for a complete set is not selling a genuine watch. There is no third option at that price.
What high-grade replicas get wrong
Better copies of the Portugieser Chronograph use a 7750-based chronograph movement with an engraved rotor. They match the case diameter. They miss the column wheel, so the pushers feel soft and the chronograph seconds hand stutters. The movement stack is taller than caliber 69355, so the case back sits high off the wrist. Copies also use 316L steel with a different polish than the IWC case.
Legal note
US law treats trafficking in counterfeit goods as a crime under 18 U.S.C. Section 2320. Customs officers can seize shipments. A counterfeit watch also carries no factory service and no parts supply.
Where to verify
An IWC boutique or service center can open the case, read the movement, and check the serial against factory records. Ask for the result in writing. A seller who refuses that step has answered the question.