The number 31610 appears in replica listings as a catalog code for the 36 mm stainless steel Ballon Bleu de Cartier with an automatic movement. It is a seller SKU, not a Cartier reference. Real Cartier references use a W-prefix format such as W69011Z4, stamped on the caseback. If a listing calls the watch a "31610" and shows no W-prefix engraving, you are looking at a first copy or a replica, not a Cartier.
That single fact settles most questions. The rest of this guide covers how to inspect the watch in hand so you know exactly what you are paying for.
What the 31610 Number Tells You
Replica factories assign short numeric codes to sort their output. A 31610 code usually points to a 36 mm case, a steel finish, a sapphire crystal, and a Chinese or Japanese automatic movement. Genuine Ballon Bleu watches in that size carry a full Cartier reference, a serial number, and matching paperwork. The code alone does not prove quality either way. It only tells you which factory batch the seller is quoting.
What You Need
- A digital caliper or a ruler with millimeter marks
- A jeweler's loupe at 10x magnification
- A bright, angled light source
- A small flathead screwdriver for bracelet screws
- A kitchen scale accurate to one gram
How to Inspect a Fake Ballon Bleu 31610
- Measure the case across the 3 to 9 o'clock line and confirm it reads 36 mm, not 35 or 38.
- Measure case thickness at the center and compare it against the 12.05 mm spec for the steel 36 mm model.
- Turn the watch over and read the caseback engraving with the loupe.
- Check that the reference starts with W and the serial is a unique eight-digit string.
- Press a fingernail against the blue cabochon in the crown and try to rotate it.
- Inspect the fluted crown under the loupe and count the ridges for even spacing and sharp edges.
- Angle the dial toward the light and look for the fine radial guilloché pattern across the whole surface.
- Read the "CARTIER" signature at the 12 o'clock position and check the spacing of the letters.
- Examine the blued steel hands for a smooth curve and a clean, rounded tip.
- Look at the date window and confirm the cut edges are square and the aperture is centered.
- Weigh the watch on the kitchen scale and compare it against the roughly 100 g expected for the steel model on a bracelet.
- Remove one bracelet screw and inspect the thread quality and the screw head slot.
- Wind the crown slowly and listen for a rough or gritty feel in the movement.
- Set the time and watch the seconds hand sweep for a stutter or a jump.
Red Flags That Settle the Question
- The cabochon spins freely under light finger pressure, which points to a glued glass bead instead of a synthetic spinel set in a gold mount.
- The caseback shows a numeric code like 31610 in place of a W-prefix reference.
- The dial print looks thick or slightly blurred under 10x magnification.
- The crown ridges feel soft or rounded rather than crisp.
- The watch weighs noticeably less than expected for a steel case and bracelet.
- The date window sits off center or the numerals look flat and printed rather than applied.
What Replicas Usually Get Right
Good first copy versions of the Ballon Bleu match the case diameter, the domed sapphire crystal, the blue hands, and the overall silhouette. Those details fool a glance from across a table. They do not survive a loupe, a caliper, or a caseback check. Judge the watch on the checks above, not on the photo in the listing and not on the seller's description.
If you want a watch that reads correctly on the wrist, spend your money on the details you can verify in hand: correct case size, crisp crown fluting, clean dial printing, and a caseback that matches the reference format Cartier actually uses.