Look at what this watch is made of. An 18K white gold case. A bezel set with two rows of white diamonds. A silvered guilloché dial. Blued-steel hands and a blue cabochon in the crown, and that is the entire colour budget.
The WE900651 is the most colourless watch Cartier makes — and Cartier clearly thought so too, because it sent this reference out on pink alligator. Not black. Some examples left the boutique on orange.
That is the whole strap question here in one sentence: on a watch with no colour of its own, the strap is the only place any can come from.
The rest of the specification: 36 mm solid white gold case, automatic calibre 076, silvered guilloché dial with black Roman numerals and an inner minute track, blued-steel sword hands, the secret Cartier signature hidden in the VII, and a fluted white gold crown set with a blue sapphire cabochon. No bracelet was ever made for it — it has always been a strap watch.
Lug Width: the WE900651 takes an 18 mm strap
On the product page, select the 18 mm option.
The 36 mm Ballon Bleu case uses an 18 mm strap, and the white gold version shares its case dimensions with the steel one. The figure is consistent across independent strap-size charts for the 36, the original Cartier strap dimensions, and the 18 mm size we stock for the model.
| Case | Strap size |
|---|---|
| 42 mm | 20 mm |
| 36 mm (WE900651) | 18 mm |
| 33 mm | 16 mm |
| 28 mm | 14 mm |
Two notes on fitting:
- Standard spring bars. This reference comes from the generation before Cartier's interchangeable bracelet system, so there is no proprietary fitting involved. A spring bar tool or our installation tool is enough.
- Tape the lugs first. Gold is softer than steel and there are stones set around the bezel. Masking tape costs nothing and a slipped tool near a diamond setting does not.
Two things worth knowing before you choose
White gold is the discreet precious metal. To anyone who does not know what they are looking at, this watch reads as steel with a diamond bezel rather than as solid gold. Many owners choose white gold precisely for that. The strap either supports that discretion or works against it.
Diamonds do not have an off switch. A set bezel is doing the same thing at breakfast as at dinner, so the only variable on the whole watch is what is underneath it. A dark strap tightens the contrast and pushes the stones forward; something with colour in it does the opposite, softening the watch and making the diamonds read as part of a design rather than as the point.
Cartier's own answer, on a watch this cold, was a coloured exotic strap. It is worth taking that seriously.
The four best straps for the WE900651
1. Blue crocodile — the colour the watch already contains
Blue Crocodile Strap for Cartier Ballon Bleu
Blue is not an outside choice on this reference: the cabochon in the crown is blue, the hands are blued steel, and the collection is called Ballon Bleu. Putting blue underneath connects those details and gives a colourless watch something to be, without the risk that a warm tone runs against white gold.
Crocodile matters as much as the colour. Cartier fitted this watch with alligator, and on a diamond-set bezel an exotic skin is the only material that answers in the same register — texture against texture, rather than a plain band under a set case. This is the closest thing in our range to how the watch was meant to look, and the most complete way to wear it.
2. Black crocodile — for the diamonds
Black Crocodile Strap for Cartier Ballon Bleu
Contrast is what makes set stones catch light, and black is the maximum. Two rows of diamonds against a black exotic strap is the most jewellery-forward configuration available here, and the most formal. If the watch is going somewhere the bezel is supposed to be noticed, this is the strap for it.
3. Blue leather — the same idea, every day
Blue Leather Strap for Cartier Ballon Bleu
Smooth blue calf gives you the same colour logic in something you will not think twice about wearing. It is less formal than the crocodile and considerably less precious, which is the point — on a watch with a diamond bezel, having one strap you are relaxed about is worth more than having two you are careful with.
4. Black leather — the discreet version
Black Leather Strap for Cartier Ballon Bleu
The quietest option on the list, and for some owners the correct one. Smooth black under white gold makes the whole watch recede: no colour, no texture, nothing signalling. If you bought white gold because you did not want the attention that yellow or rose gold brings, this is the strap that finishes that thought.
Every colour and size is in the Cartier Ballon Bleu strap collection.
Fit, in one line
Order 18 mm, tape the lugs, and fit it with standard spring bars.
More Cartier strap guides
No bracelet means the strap is the watch
Cartier never made a bracelet for this reference. The strap is not an alternative to something else — it is the only wearing part the watch has, and the only component that will ever need replacing. Alligator creases at the lug ends and darkens where it meets the skin, and against white gold and diamonds that shows sooner than it would on steel.
Helvetus straps are shaped for the Ballon Bleu case in 14 mm, 16 mm, 18 mm and 20 mm, so the leather meets the curve of the case cleanly instead of leaving the gap a generic band always leaves.
More than 50,000 customers worldwide, free shipping and free returns, and no import costs on any order, anywhere. Leather and crocodile straps are covered for one year; our rubber straps carry a lifetime warranty.
