The short answer

IW3270 is the reference prefix for the IWC Pilot's Watch Mark XVIII. The watch most people call the Mark 20 is the Mark XX, which uses IW3282 references and a 40 mm case. Replicas sold under the "IW3270 Mark 20" label are copies of that 40 mm pilot's watch, and they fall into three tiers: a cheap quartz build, a mid-tier automatic with a decorated third-party movement, and a "super clone" that copies the case, dial, and strap hardware in detail. Dials are simple to copy. Movements, crystal coatings, and caseback engraving are not. The steps below are ordered so you can rule a watch out within the first two minutes.

Prerequisites

  • Digital caliper reading to 0.01 mm
  • 10x loupe or a phone macro lens
  • Small flat screwdriver for strap removal
  • Clear photos of a genuine example for comparison

Inspection steps

  1. Measure the case across the bezel with the crown excluded. A genuine Mark XX is 40 mm. Most replicas land between 39.5 and 41.5 mm and thicken past 12 mm against the genuine 10.8 mm profile.
  2. Measure lug width and lug-to-lug span. Genuine lugs sit 20 mm apart; a wider number means the case was not cut to spec.
  3. Angle the crystal toward a light source. The genuine sapphire carries anti-reflective treatment on both faces and suppresses most reflection. Replica crystals flare blue or purple and usually lack the inner coating.
  4. Check the dial printing under magnification. The "IWC" and "SCHAFFHAUSEN" text should be sharp and spaced with intent, the 12 o'clock triangle should sit square to the dial, and the date window should be cut with clean corners over a black date wheel.
  5. Test the date change. A genuine movement snaps over within minutes of midnight. Replica date discs drift over an hour, sit off-center, or show a white wheel with black numerals.
  6. Time the power reserve. Calibre 32111 runs about 120 hours. A replica stops between 30 and 45 hours, which is the hardest spec to fake.
  7. Inspect the movement through a display back or with the caseback removed. Genuine engraving is deep and consistent. Replica rotors carry shallow laser etching, painted blue screws, and coarse perlage.
  8. Read the caseback engraving. Reference number, serial, "100m", and "SCHAFFHAUSEN" should be cut into the steel with sharp walls. Lasered or acid-etched text looks grey and flat under a loupe.
  9. Remove the strap and check the spring bar system. Watches in this line use a quick-release lug system with firm levers. Replicas use plain spring bars or a loose copy that rattles in the hand.
  10. Charge the lume with a bright light for 20 seconds. Genuine Super-LumiNova glows with an even tone across markers and hands. Replica lume is patchy, fades within minutes, and sometimes reads greener than the hands on the same dial.

Listing red flags

Listings that lead with "Swiss ETA inside", "1:1", or "mirror quality" are describing a marketing tier, not a specification. Photos showing mismatched straps, a missing reference number, or a dial with the wrong font weight are common on the same sites. Any price far under used genuine resale points to a replica, and a seller who will not send a caseback photo or a timed power reserve result is telling you what you need to know.

What the tiers mean in practice

A low-tier replica fails on the case and crystal first. A mid-tier build passes a glance and fails on the movement and reserve test. The best replicas pass the dial and case checks and still fall short on the crystal coating, the lug system feel, and long-term service parts. If a seller claims a genuine movement, ask for the calibre number and a movement photo showing the engraving depth. That single request filters most listings.

Legal and practical risk

Importing or selling counterfeit watches violates US trademark law, and shipments get seized at the border. A seized watch is gone with no refund and no recourse against the seller. A replica also cannot be serviced by the brand, holds no resale value, and often leaks well before a genuine case does. If you want the real thing, buy through an authorized dealer or a dealer with papers and a service history, and treat any "IW3270 Mark 20" listing as a replica until the checks above say otherwise.