If your Tank Must came with papers dated 2025 or later, WSTA0135 is likely the reference printed on your warranty card — it's the current number for the small Tank Must, the most accessible and most gifted watch Cartier makes. And because the reference is new, searching for it turns up almost nothing: every guide online still uses the older numbers for the same watch.
This guide fixes that. Here is the correct strap size for the WSTA0135, how it relates to the other small Tank Must references, and the straps that suit it best — including one option the larger Tanks physically cannot wear.
Cartier Tank Must WSTA0135 Strap Size and Fit
The essentials:
- Reference: WSTA0135, Tank Must, Small model
- Case dimensions: 29.5 × 22 mm, just 6.6 mm thin
- Correct strap size: 16 mm
On the product page, select the 16 mm option. The watch uses standard spring bars, so the swap takes a minute with a basic tool — and our crocodile straps even come with integrated quick-release spring bars for tool-free changes.
Two traps to avoid:
The buckle-end trap. Some spec sheets quote a number around 14 mm for this watch — that is the width at the buckle end of the factory strap, not the lug width. Order 16 mm.
The size trap. The Small and Large Tank Must are almost impossible to tell apart in photos, but the Large (33.7 × 25.5 mm — refs WSTA0041 and the current WSTA0136) takes 19 mm, and the XL takes 23 mm. If the case on your wrist measures 22 mm across, you have the Small and you need 16 mm — and that applies to every small reference: WSTA0042, WSTA0110 and this WSTA0135 are the same 29.5 × 22 mm watch under different numbers, all 16 mm.
The Entry Cartier — and Why Its Strap Matters Most
The Tank goes back to 1917, and the Must has always been its most democratic form: the Tank you actually buy, are given for a graduation, or choose as a first proper watch. The WSTA0135 carries the full signature — silvered dial, black Roman numerals, blued-steel sword hands, the beaded crown with its blue synthetic spinel — in a steel case barely 6.6 mm thin, running a high-autonomy quartz movement that asks nothing of you for years.
Cartier ships it on a black grained calfskin strap with a steel ardillon buckle. Grained calf is honest and right for what the Must is — the everyday Tank — but it is also the simplest material Cartier fits to any Tank. Which brings us to the interesting part.
The One Upgrade the Large Tanks Can't Have
Here is a quirk of strap-making that works entirely in the small Tank's favor: crocodile straps for the Tank exist only in 14 to 17 mm widths. The Large Tank Must, at 19 mm, is locked out. The Small, at 16 mm, is not.
That means the WSTA0135 — the most affordable Tank in the lineup — is one of the few that can wear the most luxurious strap material there is. The case, dial and hands are shared with Tanks costing multiples more; put crocodile where the grained calf was, and the visible difference between this watch and those disappears. These are the most popular strap choices for the small Tank Must:
1. Black Crocodile – The Upgrade That Changes the Watch
A black crocodile strap for the Cartier Tank is the single biggest jump you can make on this reference: same color as the factory strap, completely different class of material. The scales catch light the way the flat calf never could, and the watch reads dressed rather than entry-level. It ships with quick-release spring bars, so the change takes seconds. In 16 mm, this is the strap the small Tank Must was quietly waiting for.
2. Brown Crocodile – The Warm Exotic
The small Tank rarely has the wrist to itself — it lives next to gold jewellery, bangles and rings, and warm brown sits more comfortably in that company than black does. A brown crocodile strap gives the WSTA0135 the classic dress-Tank look with a softer, less formal character. At this scale, texture does the work color does on bigger watches — and brown croc has plenty of both.
3. Blue Leather – The Only Color the Watch Has
Look at the WSTA0135 closely and you'll find exactly one color: the blue of the spinel in the crown and the blued-steel hands. A blue leather strap picks up that thread and turns it into the watch's identity — subtle at a distance, obviously deliberate up close. For occasions, the same idea exists in blue crocodile as well.
4. Green Leather – Make the Most-Owned Cartier Yours
The small Tank Must is one of the most widely owned modern Cartiers — which is precisely why a green leather strap works so well on it. Green has become the Tank color of the moment, it flatters the silvered dial, and it guarantees your WSTA0135 doesn't look like everyone else's. The personality pick.
If you want to restore the exact factory texture instead, a grained black leather option is available alongside every color above in the full Cartier Tank strap collection — all in 16 mm.
Keep It Slim
One styling note that matters on this reference: the case is only 6.6 mm thick, so stay with slim, flat straps. A thick padded strap overwhelms a thin Tank and lifts it off the wrist; every strap linked above is cut flat to match the proportions Cartier designed.
Final Thoughts
The small Tank Must hands its owner exactly one decision, and it's a rewarding one — there is no bracelet, so the strap is the watch's personality, and it's the only part that will ever wear out. Helvetus is one of the leading names in the aftermarket strap world, and our Tank straps are cut to fit the 16 mm small case precisely, buckle included. Rubber straps across our range 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.
Your warranty card says WSTA0135. Your strap can say whatever you want.
