Quick answer: a fake IW371641 usually fails on four checks: case thickness, hand finishing, subdial and date layout, and caseback engraving. Measure the case with calipers (genuine runs about 13 mm thick), loupe the dial text at 10x, and read the movement through the sapphire back before you pay. Most counterfeits of this reference run 1 to 2 mm thick, use flat stamped hands, and hide a modified third-party chronograph under decorated bridges.

What a genuine IW371641 should measure

The IW371641 belongs to the Portugieser Chronograph 3716 family: 41 mm steel case, about 13 mm thick, 30 m water resistance, sapphire crystal front and back, and IWC calibre 69355 with a 46-hour power reserve at 28,800 vph. Numbers that drift from that spec are the first warning. Confirm the exact dial and case combination for IW371641 against IWC reference records, because the 3716 family has shipped several dial variants.

Prerequisites

  • Digital calipers and a small scale
  • 10x jeweler loupe or a phone camera with macro mode
  • Bright diffused light and a dark cloth to kill reflections
  • Macro photos of a known-genuine IW371641 for side-by-side comparison

Step-by-step checks

  1. Measure case diameter and thickness with calipers; expect 41 mm and about 13 mm, and treat anything over 14 mm as a fail.
  2. Weigh the watch head and compare it with a genuine steel example on the same strap type.
  3. Loupe the dial lettering; genuine print is sharp, slightly raised, and even in stroke weight, with no ink bleed.
  4. Inspect the hands at 10x; genuine hands are curved with polished bevels and a crisp profile, while fakes look flat and stamped.
  5. Check the subdial functions; small running seconds sit at 6, chronograph minutes at 12, and both hands must start and reset on command.
  6. Look at the date window at 3; numerals should be thin, centered, and matched to the dial font, with no white border and no off-center cut.
  7. Start, stop, and reset the chronograph; the central seconds hand should snap back to zero without stutter or overshoot.
  8. Read the caseback engraving; reference number, serial, and the International Watch Co. script should be deep, crisp, and correctly spelled.
  9. Examine the movement through the display back; compare finishing, screw heads, and rotor engraving against macro photos of calibre 69355.
  10. Work the crown and pushers; winding should feel smooth with no grit, and each pusher should travel with a firm click and no wobble.
  11. Check the strap and buckle; stitching density, alligator grain, and the signed buckle engraving all matter on this price tier.
  12. Match the caseback serial to the warranty card and service paperwork before any money changes hands.

Common tells on counterfeit IW371641

  • Case too thick, with lugs that feel slab-sided in the hand
  • Blue-tinted crystal from single-side anti-reflective coating
  • Subdial at 12 that counts tenths of a second instead of chronograph minutes
  • Shallow laser engraving on the caseback and a repeated serial number
  • Bold or misaligned date numerals
  • Rotor that spins loudly and wobbles when the watch is tilted
  • Box, papers, and hangtag that use the wrong fonts and paper stock

What a replica can and cannot copy

Good replicas get the outer case proportions close, and the 41 mm size plus the two-subdial layout is easier to fake than a three-register dial. The gap shows in the details: hand finishing, print quality, engraving depth, and the view through the back. No replica carries an IWC warranty or a service history, so price a replica as a replica. If a seller asks genuine money for a watch with a 14 mm case and flat hands, walk away.