Top pick: a 41 mm Portugieser Chronograph clone with a column wheel style chronograph movement, a twin register dial (running seconds at 6, chronograph minutes at 12), and a midcase that matches the IW3716 footprint. The criteria below cover case diameter and thickness, dial furniture and subdial placement, movement behavior and pusher feel, crystal and caseback detail, and strap hardware. A version that places the registers wrong cannot be fixed later, so that check comes before everything else.

What the IW371631 Represents

The reference belongs to the Portugieser Chronograph line, the clean two register design IWC has built for decades. The current generation uses a 41 mm case, feuille hands, applied Arabic numerals, a rail track minute ring, and the in house 69355 chronograph calibre with a column wheel and a power reserve in the region of 46 hours. Water resistance across the line is modest, rated for rain and hand washing rather than swimming. Dial color, case metal, and small details move between variants, so confirm the exact 371631 configuration against the maker's product listing before you compare any replica photo with it.

Criterion 1: Case Size and Profile

The Portugieser look depends on a wide, thin case with a narrow bezel and lugs that curve down toward the wrist. This is the first thing a replica gets wrong, and it is visible from across a table.

Pros of a correct case

  • 41 mm diameter sits flat on a 6.5 to 7.5 inch wrist without overhang.
  • Brushed flanks with a polished bezel and polished lug tops read correctly in daylight.
  • Correct lug width lets you fit a genuine spec strap later.

Cons to watch for

  • Oversized cases listed as 42 mm or more, which change the silhouette.
  • Thick midcases that sit tall and hide the slim bezel line.
  • Caseback rims that stand proud and create a gap against the wrist.

Best for: buyers who wear the watch daily and care about how it sits under a shirt cuff. Measure your wrist and compare against the listed dimensions before ordering.

Criterion 2: Dial Layout and Subdial Positions

Twin registers at 12 and 6 are the signature. Running seconds sit at the bottom, chronograph minutes at the top, and the spacing between them should leave a clear band of dial across the middle. If the reference has no date, a date aperture at 3 o'clock is an instant tell.

Pros of a correct dial

  • Applied numerals with polished edges and clean white fill.
  • Feuille hands at the right length, reaching the inner edge of the minute track.
  • Print weight and spacing that hold up under a loupe at arm's length.

Cons you will see

  • Registers pushed toward the center, leaving a wide empty ring.
  • Flat stamped hands with blunt tips.
  • Text that drifts in size or spacing between the model lines.

Best for: anyone who wears the watch in public. This is the single highest value check in the whole guide.

Criterion 3: Movement and Chronograph Function

Ask what the movement does, not what it is called. Start the chronograph, let it run for several minutes, and watch the top register. It should advance in one minute steps and reset to zero with a firm push.

Pros

  • Column wheel style actuation with a light, clean pusher click.
  • Seconds hand reset that lands at 12 without drift.
  • Rotor that winds with wrist movement and stays quiet.

Cons

  • Registers that count hours instead of minutes, which breaks the dial.
  • Stiff pushers or a reset that overshoots.
  • Sweeping seconds with visible stutter or a rotor you can hear across a room.

Best for: buyers who actually use the chronograph. If you never touch the pushers, spend the money on the dial and case instead.

Criterion 4: Crystal, Caseback, and Engraving

Sapphire front and back with an anti reflective coating on the inside is the baseline. Under the caseback you should see a decorated movement with a signed rotor, and around the rim you should see reference, movement, and water resistance engraving cut into the metal rather than printed on it.

Pros

  • Crystal that stays clear at shallow angles with no milky haze.
  • Display back that frames the movement and shows finishing on the bridges.
  • Engraving that looks deep and even under a light.

Cons

  • Mineral glass that scratches within weeks.
  • Shallow laser etching that disappears in photos.
  • Solid casebacks hiding a plain movement on versions sold as display back models.

Best for: collectors who flip the watch over and inspect it. If the back matters less to you, this is where a budget build can be forgiven.

Criterion 5: Strap and Clasp

The line is sold on leather, so the strap carries a lot of the look. Check stitching density, edge paint, and whether the clasp matches the case metal tone.

Pros

  • Alligator pattern leather with fine, even stitching.
  • Tang or deployant clasp with a crisp, centered stamp.
  • Spring bars that release without gouging the lugs.

Cons

  • Stiff corrected grain leather that creases sharply in a week.
  • Clasp metal that reads yellow against a steel case.
  • Oversized buckles that dwarf the 20 mm lug width.

Best for: buyers who plan to wear it on day one. Budget for a replacement strap if the stock one feels thin.

Market Tiers and What They Buy You

Budget tier

Low cost, quartz or basic automatic inside, dial accuracy that varies batch to batch. Pros: cheap enough to test the look. Cons: wrong thickness, weak lume, obvious hands. Best for a first trial run.

Mid tier

Correct case size, better dial printing, a working chronograph with the right register layout. Pros: the best balance of price and accuracy. Cons: movement finishing and caseback detail still fall short. Best for most buyers.

Top tier

The builds that hobby forums compare side by side with the genuine article. ZF is the name most often attached to IWC Portugieser replicas in buyer threads, so treat the name as a starting point and judge the actual photos. Pros: correct proportions, clean dial, solid pusher feel. Cons: highest cost, and quality still varies between batches. Best for buyers who want the closest match and will inspect it closely.

Use Case Recommendations

  • Office and dress wear: mid tier with a correct dial, on leather.
  • Weekend and travel: top tier, since case finishing holds up under hotel lighting and photos.
  • First replica and unsure: budget tier to confirm the size works on your wrist.
  • Gift or resale context: skip the replica category entirely.

Pre Purchase Checks

  1. Confirm the exact 371631 dial color and case metal from the maker's listing.
  2. Ask for a straight on dial photo and a profile photo side by side.
  3. Request a short video of the chronograph starting, running, and resetting.
  4. Ask for the measured case diameter, thickness, and lug width.
  5. Check the return policy before payment and keep the conversation record.