What size strap does an Airain Sous-Marine take?

20mm at the lugs. All six Sous-Marine product pages, from the Re-Edition Lollipop and DNA Strand to the Deep Blue, Faded Black, Tropical and Ocean Green editions, print the same all-caps line: DIAMETER 37.5MM (CASE) / 38.2MM (BEZEL), LUG WIDTH 20MM, LUG-TO-LUG: 48.2MM. The embedded spec sheet on the same pages independently lists Lug width: 20mm.

Do all Airain watches take a 20mm strap?

Every Airain product page that prints a width prints 20mm, but three of the fourteen watch pages print no width at all: the Type 20 Up in the Air x Seconde Seconde collaboration (427.406), the Type 20 ACE (428.440) and the Type 20 70 Ans (421.702). For those three, measure the watch or ask Airain directly rather than assuming 20mm from the rest of the catalog.

Why does the Airain spec sheet say 18mm?

Because that 18mm is the buckle end, not the lug width. The Sous-Marine spec sheet reads Buckle type: pin buckle, Size: 18mm, and Airain's own strap shop lists its 20mm rubber straps with Buckle width: 18 mm. The strap tapers from 20mm at the lugs to 18mm at the buckle. If you buy a straight 18mm strap for a Sous-Marine it will not fit the lugs.

Airain band size chart: one width, three vocabularies, three silences

Airain sells fourteen watches through its WordPress storefront, and if you went looking for a strap size chart you already know the brand does not publish one. What it does publish is specification text in three different vocabularies depending on the family, and three watches whose pages print no width at all [1]. This chart comes from rendering all fourteen watch pages and reading every width line, in every vocabulary, at build time.

Scope, stated up front

The Airain product sitemap lists 38 product URLs [1]. Fourteen are watch product pages. The other twenty-four are accessories: twelve FKM rubber straps, four suede straps, three leather straps, two buckles, a crown cap, a Fixoflex bracelet and a reproduction poster. Those accessory pages are excluded from this chart; their widths describe the straps themselves, not watch lugs. Of the fourteen watch pages, eleven print a strap width and every single one of them prints the same number: 20mm. The remaining three print none. There is no second width anywhere in the catalog, which makes this the rarest kind of brand chart, the one-width kind, and the only trap left is vocabulary.

The chart, all fourteen watches

Watch	Reference	Lug width	Attested how
Sous-Marine Re-Edition Lollipop	524.437A	20mm	All-caps case rail and spec sheet [2]
Sous-Marine Re-Edition DNA Strand	524.437B	20mm	All-caps case rail, spec sheet and bracelet line [3]
Sous-Marine Deep Blue	524.422	20mm	Limited edition; same three attestations [3]
Sous-Marine Faded Black	524.407	20mm	Limited edition; same three attestations [3]
Sous-Marine Tropical	524.457	20mm	Limited edition; same three attestations [3]
Sous-Marine Ocean Green	524.481	20mm	All-caps case rail and spec sheet [3]
Type 20 Re-Edition	421.436S	20mm	Spec spans plus embedded schema description [4]
Type 21	423.438	20mm	Spec spans plus embedded schema description [5]
Type 20 Furtivité	421.889	20mm	Limited edition; spec spans plus schema [6]
Voyageur GMT	721.419	20mm	All-caps STRAP WIDTH block, printed twice [7]
Voyageur GMT	721.432	20mm	All-caps STRAP WIDTH block, printed twice [8]
Type 20 Up in the Air x Seconde Seconde	427.406	none printed	No width text rendered on the product page [9]
Type 20 ACE	428.440	none printed	No width text rendered on the product page [9]
Type 20 70 Ans	421.702	none printed	No width text rendered on the product page [9]

Eleven attested at 20mm, three silent, zero contradictions. The three attestation vocabularies are documented below, because a buyer who learns one of them will misread the others.

Sous-Marine: the all-caps case rail

All six Sous-Marine pages carry the same all-caps line in the case description block: DIAMETER 37.5MM (CASE) / 38.2MM (BEZEL), LUG WIDTH 20MM, LUG-TO-LUG: 48.2MM [2][3]. That line is the strongest attestation in the catalog: it names the measurement as the lug width, it is visible on the rendered page, and all six variants agree byte for byte. The same pages embed a second spec sheet in the page source, which reads, with line breaks shown as slashes: Strap / Lug width: 20mm / Strap: quick-release Tropic-style FKM rubber strap / Buckle type: pin buckle / Size: 18mm [2]. Note what is missing from that sentence and what is not: the 18mm sits directly beside the buckle type, and it is covered in its own section below. Five of the six Sous-Marines also render a bracelet line reading FixoFlex® stainless steel bracelet 20mm Both included, a third confirmation of the width on the bracelet side [3]. The Re-Edition Lollipop ships the FKM strap only, so its page shows the strap line without the Both included sentence.

Type 20 and Type 21: lowercase spans plus an embedded schema

The three 39mm monopusher pages, the Type 20 Re-Edition 421.436S, the Type 21 423.438 and the Type 20 Furtivité limited edition 421.889, print their width in ordinary sentence case inside the specification block: Genuine leather strap in Midnight Blue Lug width: 20mm Size: 18mm [4][5][6]. The same 18mm buckle pairing as the Sous-Marines is at work here too. Each of these pages also embeds a structured-data description in its source that ends the strap paragraph with Lug Width: 20mm, capital W, a second attestation surface on the same page [4]. Their case block reads Diameter: 39mm Height: 10,5mm Lug-to-lug: 47,35mm, comma decimal separators and all, and the lug-to-lug figure is quoted here as context only: it is a length over the lugs, never a width [4].

Voyageur GMT: the all-caps STRAP WIDTH block

The two Voyageur GMT pages, 721.419 and 721.432, print no Lug width line at all. Their specification block uses a third vocabulary, all-caps labels with values in bold: STRAP White/grey suede leather STRAP WIDTH 20MM BUCKLE 316L stainless steel buckle [7][8]. The block appears twice on each page, once in the specifications and once in the description, and both occurrences agree. STRAP WIDTH here is the strap's width at the lugs, the same 20mm the rest of the catalog attests; the BUCKLE line that follows names the buckle material, not a width.

The three that print nothing

Three watch pages render no width text whatsoever, and this chart will not guess for them. The Type 20 Up in the Air x Seconde Seconde collaboration, reference 427.406, the Type 20 ACE, reference 428.440, and the Type 20 70 Ans, reference 421.702, were each pulled and scanned in full: no lug width, no strap width, no width in any vocabulary, in either the rendered text or the embedded schema [9]. Given that the other eleven watches in the catalog are all 20mm, 20mm is the reasonable expectation for these three, but expectation is not attestation. Measure between the lugs, or ask Airain, before buying.

The 18mm is the buckle, never the lug

The one number on Airain spec sheets that can mislead a strap buyer is 18mm. On the Sous-Marine embedded spec sheet it reads Buckle type: pin buckle, Size: 18mm, sitting right after the strap line that already said Lug width: 20mm [2]. Airain's own accessory shop settles what that 18mm is: the FKM rubber strap product page, the strap the Sous-Marines ship on, lists Strap size (lug): 20mm Strap length: 8cm + 13cm Buckle width: 18 mm [10]. The strap is 20mm at the lugs and tapers to 18mm at the buckle. A buyer who reads Size: 18mm as the strap width and orders a straight 18mm strap has bought a strap that will not span the lugs of any watch in this catalog.

Why no incumbent chart exists

Search for an Airain band size chart and the results are the brand's own product pages, generic strap sizing guides that never mention Airain, and dealer listings. The watchbands.ai brand index, pulled fresh for this build with its Seiko, Citizen and Rolex controls firing across 193 brands, does not list Airain at all [11]. The closest third-party signal is a Chrono24 dealer listing for the Sous-Marine Tropical that independently prints lug width 20 mm, which corroborates the number without being a chart. Nobody, including Airain, maps the models to the width. This page does, from first-party pages only.

How this chart was checked

At build time, 1 October 2026, the Airain sitemap index and product sitemap were pulled fresh: 38 product locations, 14 of them watch pages [1]. All fourteen watch pages were then pulled with a browser user agent and scanned in full: rendered text, embedded spec sheets and schema descriptions. Eleven pages attest 20mm across three vocabularies, three pages attest nothing, and no page attests any other width. Every quotation on this page was machine-matched as a contiguous run against the bytes it was pulled from, with embedded line breaks shown as slashes. No width was taken from a lug-to-lug figure, a buckle size, or the nearest round number, and the three silent pages are disclosed as silent rather than filled in. For the brand universe around it, the watch band size chart carries Airain beside every other brand charted here, and the lug width chart by brand holds the expanded per-brand table.