Replacement FKM Rubber Strap for Cartier Santos WSSA0018 – QuickSwitch 21mm

Product Overview

Fuerman makes this 21 mm strap for the Cartier Santos de Cartier large case — the 39.8 mm model with the QuickSwitch release built into the lugs. It is shaped for that case alone rather than being a universal band trimmed to fit, so the ends meet the lugs squarely and the strap sits flush instead of lifting at the corners.

The strap is moulded from FKM fluororubber, a dense matte rubber that stays soft through daily wear, resists sweat, UV and heat, and holds its shape far longer than natural rubber. Two equal 115 mm halves carry a folding clasp, and the pair weighs about 22 g, so the watch keeps its slim profile on the wrist. Black, Blue, Orange and Gray are stocked; each colour can be ordered on its own or with a buckle finished in silver, gold or rose gold.

Swapping straps is a matter of seconds: press the QuickSwitch release at the lug, slide the original strap out and click the new one in. No spring-bar tool is needed and nothing touches the case. Many owners keep the steel bracelet for formal days and wear this rubber strap for everything else — travel, sport, hot weather and wet weekends.

Like the other custom fluororubber material watch straps we produce, this one is engineered around a single case geometry and a single fitting standard. It is an aftermarket replacement strap, not a Cartier product.

Specifications

QuickSwitch Fit & Installation

1. Check the caseback reference first. This custom fluororubber material watch strap is cut for the Santos large case and its 21 mm lug width, so the quick-release ends are shaped for that case geometry and nothing else.
2. Lay the watch face down on a soft cloth. A microfibre cloth or a folded towel keeps the crystal and the polished case edges clear of the work surface while you work.
3. Press the QuickSwitch release at each lug and slide the original strap out. The same action releases both ends, so no spring-bar tool is required at any point.
4. Slide the new end into the lug until the quick-release spring bar seats itself, then tug it gently to confirm it is locked.
5. Repeat on the other side, then look across the case: both ends should meet the lugs with no gap and no lifted edge, and the strap should run straight rather than twisting to one side.
6. Refit your folding clasp if you ordered the strap-only version, or check the buckle if you ordered one, and press the release one last time to confirm it moves freely before you wear the watch.

Equal-Length Layout & Wrist Fit

• Two equal halves: both sides measure 115 mm, so the folding clasp lands close to the centre of the wrist instead of sitting off to one side as it does on an asymmetric strap.
• Steadier on the wrist: because the clasp stays over the flat of the wrist, the watch is less likely to rotate during the day, which counts on a square case that carries a heavy bracelet heritage.
• Built for average to larger wrists: the 115 + 115 mm layout leaves a balanced amount of strap on both sides of the clasp, and a fluororubber material watch strap holds that shape rather than stretching out of it.
• Slim profile: at 1–3 mm thick and 22 g for the pair, the strap slips under a shirt cuff and keeps the watch sitting low on the wrist.
• Consistent over time: FKM keeps its length and softness, so the position of the clasp on the wrist does not drift as the strap ages.
• Quick check when you put it on: with the watch fastened, look at both ends — they should meet the case at the same angle. If one side looks longer, the clasp simply needs repositioning.

FKM Fluororubber: Material & Build

The strap is moulded from FKM fluororubber, the fluorine-based rubber chosen where ordinary rubber would not last. It resists sweat, UV light, heat and the chemicals of everyday life, and it does not go brittle, crack or peel the way natural rubber eventually can. That is why the custom fluororubber material watch straps we produce are the ones we suggest for warm, humid climates and for watches that are worn hard all week.

In the hand it feels dense and faintly matte, with a smooth surface rather than a tacky one. It does not grip the skin in hot weather, and it softens against the wrist as it warms, which is what makes the watch comfortable on a long day. FKM is also the kinder choice for sensitive skin: it does not harden and trap moisture the way cheaper rubber does.

Build quality shows at the ends. The quick-release fittings are moulded to match the case, so the strap meets the lugs squarely, and the 1–3 mm body gives it enough substance to hold a clean line without feeling stiff. At 22 g for the pair, the watch does not become noticeably heavier on the wrist.

The matte surface keeps glare and fingerprints to a minimum and stays even in tone across the whole strap, including the areas that see the most contact.

Colour & Buckle Options

Everyday Wear & Care

• Rinse after water and sweat: fresh water after the sea, a pool or a hard workout, then pat the strap dry with a soft cloth. Salt and chlorine shouldn't be left sitting on any strap.
• Deeper cleaning: wash this custom fluororubber material watch strap in lukewarm water with a little mild soap and a soft brush, rinse it well and let it dry completely before refitting.
• Skip the harsh products: solvents, alcohol-based sanitisers, abrasive polishes and metal brushes will dull the surface long before the rubber itself wears out.
• Dry it properly: air-dry at room temperature, away from radiators and direct sun. Heat is what shortens the working life of a rubber strap.
• Store it flat: keep a spare strap flat or loosely rolled in a drawer or watch roll rather than folded tightly under the watch.
• Watch the everyday contacts: sunscreen, insect repellent and hand cream are the usual causes of a dull patch, so wipe them off when you notice them.
• Check the fitting: every few months press the QuickSwitch release once and let it re-seat, which clears grit and keeps the mechanism crisp.

Ordering & Fit Confirmation

1. Check your case reference: this strap is made for the Santos large case with the 21 mm lug width shown in the specifications. If your Santos is a different size, this is not the strap for that watch.
2. Choose the finish: Black, Blue, Orange or Gray.
3. Choose the buckle: strap only, so you refit your original folding clasp, or supplied with a buckle in silver, gold or rose gold.
4. Think about the length: the 115 + 115 mm layout is built to sit evenly on average to larger wrists. If your wrist is on the slim side, note it in the order comments.
5. Know what arrives: the strap, plus a buckle only if you selected one. The quick-release spring bars are part of the strap ends, so no separate fittings are needed.
6. Order this watch strap online, then fit it on arrival — the QuickSwitch release makes it a minute's work with no tools.
7. Buying several straps, or ordering for a shop? Ask us about current availability and quantity pricing before you order.
8. If you need the strap by a particular date, confirm the current lead time, packing and shipping terms with us before placing the order.

Technical Support & Model Matching

FUERMAN has been supplying watch parts and accessories from Huadu District, Guangzhou since 2010 — 15+ years in the trade, a 60-strong team and a deep ready stock held in China. Our technical team, which includes technicians with 30+ years of watchmaking experience, matches items to your watch by brand, model or reference number before you order, so you know it will fit. Send a photo or a measurement if you are unsure: we will confirm the right choice, talk you through fitting, and stay with you afterwards — troubleshooting, replacement parts and after-sales help long after your order arrives.

FAQ