Answer first

“33660” is not a Cartier reference. It is a common typo for 3366, the case reference engraved on the 42 mm Ballon Bleu de Cartier automatic sold as W69012Z4. A fake Ballon Bleu 33660 is therefore a replica of that 42 mm steel watch. Judge it in this order: case size and shape, crown cabochon, dial and guilloché, caseback engraving, movement, then bracelet fit. The first three decide whether it passes at arm's length. The last three decide whether it passes in the hand.

Prerequisites

  • Digital calipers that read to 0.1 mm.
  • A 10x loupe or a phone camera with 5x to 10x zoom.
  • Neutral 5000K light and a clean, non-scratch mat.
  • Reference photos of a genuine 42 mm Ballon Bleu: front, crown side, caseback, clasp.
  • The seller's listed spec: case diameter, movement name, crystal type, weight.

Step-by-step inspection

  1. Place the watch face-up under 5000K light and take a straight-on photo at 10x zoom. Keep the camera level with the dial so you can compare proportions later.
  2. Measure the case across the bezel from 12 to 6 and again from 9 to 3. A 42 mm Ballon Bleu should read close to 42.0 mm both ways. Anything under 41.4 mm or over 42.6 mm is the wrong case.
  3. Turn the watch to the crown side and check the cabochon. The genuine 3366 uses a blue synthetic spinel set in a fluted crown guard. Replicas often use glass or dyed plastic that looks purple in shade or too bright in sun.
  4. Run a fingernail along the lug curve from the caseband to the tip. The genuine lug is a smooth continuous arc. A replica often has a flat spot or a sharp transition where the lug meets the case.
  5. Look at the dial at 10x. The guilloché should be cut, not printed, and the Roman numerals should sit inside the minute track without touching it. Check the “VII” and “IX” for thick or uneven strokes.
  6. Check the date window at 3 o'clock. On the 42 mm 3366 the window is square with a clean bevel and the date sits centered. Off-center dates and rounded corners are common replica faults.
  7. Read the caseback engraving. The reference number, serial, and “Swiss Made” should be crisp and evenly spaced. Laser-etched replica text looks shallow and fuzzy under a loupe.
  8. View the movement through the caseback. A credible 42 mm replica runs a clone of the Cartier 049 (ETA 2892-A2 base) or a decorated Miyota. A rough rotor, plastic movement ring, or no visible jewels means a low-tier build. Note that the 42 mm 3366 is time-only, so there is no sweeping seconds hand to judge.
  9. Check the bracelet fit. End links should sit flush to the case with no gap wider than a hair. The clasp should close with one firm press and the folding parts should not rattle.
  10. Weigh the watch on a kitchen scale. A steel 42 mm Ballon Bleu on bracelet sits around 140 to 155 g. A watch under 120 g usually has a hollow case or a lightweight bracelet.

Red flags at a glance

  • Cabochon that looks purple, cloudy, or too tall.
  • Printed guilloché that looks flat under a loupe.
  • Date window with rounded corners or an off-center date.
  • Lug tips that feel sharp or sit above the caseband.
  • Caseback text that is shallow, wide, or misaligned.
  • Rotor that spins loosely and sounds like a coin in a can.

What a credible 1:1 should include

A serious 42 mm Ballon Bleu replica should list the case diameter, the movement base, sapphire crystal with anti-reflective coating, and the cabochon material. Ask for a clear photo of the caseback and a short video tilting the watch to show crystal reflections and dial depth. If the seller cannot provide those two files, treat the listing as unknown quality.

Bottom line

Reference 3366 is a simple watch to fake badly and a hard watch to fake well. Check size, cabochon, dial, and caseback before you look at the price. A correct 42 mm case with a clean dial and a properly finished movement is the minimum for a wearable replica. Anything less is a costume piece.