The short answer
A replica Clé de Cartier medium is a 35mm copy of Cartier's key-crown dress watch. The best versions get the case profile, dial layout, and crown shape close enough that only a jeweler with a loupe would catch it at arm's length. The weak versions show up in three places: a crown that feels loose or sits proud of the case, a dial that's printed soft or too glossy, and a case that runs a millimeter or two too thick. Judge those three things first, then worry about everything else.
What "medium" means
Cartier builds the Clé in 31mm, 35mm, and 40mm. Medium is 35mm, and it's the size most buyers want because it wears like a classic dress watch on an average wrist. The genuine medium runs an automatic movement and sits around 10mm thick, so a replica that measures 12mm will look and feel wrong the moment you put it on. Ask for caliper photos with the watch off the wrist. Sellers who won't send them are telling you something.
Reference numbers matter too. Some medium references have a date at 3 o'clock and some don't, and the dial texture changes between the flinqué (engine-turned) versions and the plain ones. Pick a reference and match it. A replica with a date window where the real one has none is an easy tell.
The crown is the whole point
The Clé is named for its crown, which is shaped like a key and winds the way one turns in a lock. That detail is also the hardest part to copy well.
- Cabochon: real ones use a sapphire or spinel. Cheap replicas use glass or dyed resin that looks flat in daylight.
- Seating: the crown should sit flush and turn with light, even resistance. Gritty or wobbly means a cheap stem and tube.
- Shape: the key head should be crisp, not rounded off from over-polishing.
Movement and thickness
Replicas come with three basic movements, and the price tracks them closely.
- Quartz. Cheapest, thinnest, and the second hand ticks instead of sweeping. Fine for a $100 watch, wrong for a $4,000 one.
- Miyota-based automatic. The sweet spot for most buyers. Reliable, serviceable, and it sweeps properly.
- Decorated clone automatic. Bridges engraved to mimic Cartier's in-house caliber. Pretty through a display back, no better at keeping time.
Dials, hands, and finishing
Look at the printing under magnification. Roman numerals should be sharp, the railroad track should be even all the way around, and the hands should be polished on the bevels with a matte top surface. Cartier hides a small signature inside one of the numerals on many references, and replicas either miss it or make it obvious. Case finishing should mix polished and brushed surfaces with a clean line between them. If the whole case is mirror polished, it's wrong.
Gold plating is usually 2.5 to 5 microns on the better replicas. Thin plating wears through at the lugs within a year of daily wear. If you want the gold look long term, ask about plating thickness or buy steel.
Quick checklist before you pay
- Caliper photo of case diameter and thickness.
- Close-up of the crown from three angles.
- Macro shot of the dial printing and the hidden signature.
- Movement photo, plus timing numbers on a timegrapher.
- Caseback engraving and screw heads, which should be clean and undamaged.
- Strap or bracelet quality, since that is often where the money was saved.
One thing worth saying plainly
A replica is a copy, not a Cartier. Cartier won't service it, it has no value as a genuine piece, and passing one off as real is fraud. Buy it as what it is, wear it as what it is, and you won't have a problem.