The Cartier Santos W4SA0006 is what happens when Cartier's jewelers and watchmakers agree on something: a graduated blue dial framed by 206 brilliant-cut diamonds — in effect, a sapphire-and-diamond ring you can read the time on. It's the blue-dial twin of the silver diamond Santos, built on the same 100-meter QuickSwitch case, and it ships with a steel bracelet plus a blue alligator strap in the box.
Which means the strap question here is really a jewelry question — and jewelry has rules. Correct size first.
Cartier Santos W4SA0006 Strap Size and Fit
The essentials:
- Reference: W4SA0006, Santos de Cartier, Medium model, diamond-set bezel, graduated blue dial
- Case width: 35.1 mm
- Correct strap size: 19 mm, made for the Cartier QuickSwitch system
On the product page, select the 19 mm option. Both factory options on this reference use QuickSwitch, and so do our straps — they click straight into the case in seconds, no tools, no contact with the diamond bezel. A generic 19 mm strap will not attach; the QuickSwitch fitting in the strap end is what locks it in.
Don't size by dial color: Cartier also makes graduated blue dials on the Large case (39.8 mm — refs WSSA0013, WSSA0030 and WSSA0071), and those take 21 mm. The diamond bezel is your tell: every diamond-set medium — this blue, the silver version, and the earlier WJSA-numbered pieces — is the 35.1 mm case, and every one takes 19 mm.
A Sapphire With a Halo
Strip away the stones and this is the modern Santos at its best: caliber 1847 MC automatic, the seven-sided crown with its faceted blue spinel, sapphire crystal, SmartLink bracelet, 100 meters of water resistance. Then the two signatures. The dial is a graduated blue sunray — deeper at the edges, lighter at the center, shifting with every turn of the wrist — with raised metallic Roman numerals and luminous silver-tone sword hands. And around it, the bezel carries 206 diamonds totaling 0.64 carats, following the Santos screws all the way around.
In jewelry, that arrangement has a name: a halo. A ring of diamonds set around a blue stone exists to do one job — make the center look bigger, deeper, and bluer. Cartier built exactly that geometry into this watch. The strap decides whether the halo gets to work.
Make the Halo Work
Here's the mechanism. A halo performs against a calm ground: dark and quiet beneath the case, and the blue reads richer while the diamond ring burns brighter by contrast. Put the same watch on the polished bracelet and the halo has competition — hundreds of steel facets flashing alongside 206 diamonds — and the effect dissolves into general shine. Beautiful, but no longer a halo.
These are the most popular strap choices among diamond Santos owners:
1. Black Leather – The Ground the Halo Needs
A black leather strap for the Cartier Santos is the definitive strap for this reference: matte black under the case removes every competing gleam, the graduated blue deepens toward sapphire, and the diamond ring becomes the single brightest thing on your wrist. It's the jeweler's display principle, worn. Formal enough for anything, and compatible with the original Cartier buckle if you prefer to keep using it.
2. Black Rubber – Diamonds That Can Swim
The case under those stones is rated to 100 meters — and neither the factory alligator nor a polished bracelet wants to prove it. A black rubber strap is how this watch does summer: pool, beach, travel, while both factory options stay flawless in the box. Matte rubber grounds the halo exactly like the leather does, just in sport form — and every Helvetus rubber strap carries a lifetime warranty.
3. Blue Leather – The Everyday Twin of the Factory Strap
Cartier already answered the tonal question by putting a blue alligator in the box — but alligator is for occasions, not for daily creasing. A smooth blue leather strap keeps the blue-on-blue look Cartier intended for every day, saving the factory strap for the evenings it was made for. Think of it as the working version of the strap you already own.
4. Brown Leather – Navy and Tan, With Fire
The adventurous pick: warm brown against the graduated blue is the classic navy-and-tan pairing, and the diamonds turn it luxurious rather than casual — white fire over warm leather is its own kind of statement. This is the brown leather strap for the owner who wants the one combination nobody expects on a diamond watch, and it's the single warmest look this reference can wear.
Every compatible option — more leather colors and rubber tones in 19 mm — is in the full Cartier Santos strap collection.
Protect the Set
Three things came in your box: the SmartLink bracelet, the blue alligator, and the watch itself. Straps are how all three stay perfect — the bracelet avoids desk-diving hairlines, the alligator avoids daily creasing, and on a diamond reference, a complete unworn factory set matters most of all. If you remove bracelet links, store them together.
Final Thoughts
The W4SA0006 is Cartier's sapphire-and-diamond idea, engineered to be worn anywhere — and the strap is what completes the setting. Helvetus is one of the leading names in the aftermarket strap world, and our Santos straps are made specifically for the QuickSwitch system: an exact 19 mm fit, no tools, no guesswork. Rubber straps carry a lifetime warranty, shipping is free worldwide with no import costs, and more than 50,000 watch owners already trust us with their straps.
Cartier set the halo. The right strap is what makes it burn.
