What size strap does a JIOS watch take?

Four widths cover the whole English-store catalog, and every one is stated by the maker on the watch's own page. GMT Diver's 104 takes a 20mm strap, printed as Lug width: 20mm, on all 7 of its dial listings. Seiran takes 18mm across all 49 of its listings and Biwa takes 18mm across all 12 of its listings, both printed as Lug width: 18mm. Awazu takes a 14mm strap, printed in its own word order as the width between lugs: 14mm, on all 20 of its listings. Omi is the exception that needs reading: its English pages print the width between lugs: 38mm, which is a mistranslated lug-to-lug span, and the maker's Japanese page for the same watch states the band lug width as 18mm. Buy 18mm for an Omi.

The Omi page says the width between lugs: 38mm. Do I need a 38mm strap?

No, and the number contradicts itself on its own page. The Omi case is stated as approximately 35x35x9mm excluding lugs and crown, and a 38mm strap cannot physically attach between the lugs of a 35mm case. The maker's Japanese product page for the same watch prints the full block: case diameter approximately 35mm, lug-to-lug 38mm, band lug width 18mm. The English page dropped the lug-to-lug label and pasted its 38mm value into the width-between-lugs position, so the 38mm is the tip-to-tip span of the case, not the gap the strap fills. The strap size for every Omi listing is 18mm.

Is the width between lugs the same thing as lug width on this site?

Not always, and this catalog is the proof. JIOS prints its width line in two word orders: the round-case lines, GMT Diver's 104, Seiran and Biwa, print Lug width: with the label first, while the cushion-case lines, Awazu and Omi, print the width between lugs: with the value first. On Awazu the two forms agree: the English page says the width between lugs: 14mm and the Japanese page for the same watch says lug width 14mm, so 14mm is the strap size. On Omi the value-first line carries the wrong number entirely, the lug-to-lug 38mm, while the Japanese page's band lug width line says 18mm. So the word order tells you which family you are reading, and only the cross-language check tells you whether the number is a width.

Will the replacement straps JIOS sells fit every model?

No. Every replacement strap in the English store is an 18mm strap: the product pages state it twice, once as This replacement watch strap (18mm lug width) and once in the spec block as Dimensions Lug width: 18mm. That fits Seiran, Biwa and Omi, the three 18mm families. It does not fit the GMT Diver's 104, which needs 20mm, and it does not fit the Awazu cushion case, which needs 14mm; at build the English store sells no first-party strap in either of those widths. The Japanese store adds a pair watch, the Awazu no Seiran, that splits by wrist: the same 28x28mm cushion case ships with a men's band at 18mm and a women's band at 14mm, so even one product can need two sizes.

JIOS band size chart by model

JIOS is an independent Japanese watchmaker operating out of Ishiyama, Otsu City, Shiga Prefecture, the historically claimed birthplace of Japanese watchmaking, and its catalog splits into five families that need exactly three strap widths: 20mm for the GMT Diver's 104, 18mm for Seiran, Biwa and Omi, and 14mm for the cushion-case Awazu ^[1]. Every width is printed by the maker on every watch page of the English store, 94 watch listings in total, in spec blocks this chart quotes verbatim ^[5]. One trap sits in the middle of the map: the Omi pages print the width between lugs: 38mm on a 35mm case, and the maker's own Japanese page for the same watch proves that 38mm is the lug-to-lug span with the real band width stated as 18mm ^[6].

Quick answers: GMT Diver's 104, 20mm on all dials ^[1]. Seiran, 18mm across all 49 listings ^[2]. Biwa, 18mm across all 12 listings ^[3]. Awazu, 14mm, printed as the width between lugs: 14mm ^[4]. Omi, 18mm per the maker's Japanese spec; the English 38mm figure is a mistranslated lug-to-lug, never a strap size ^[5]^[6]. The store's own replacement straps are all 18mm and fit the three 18mm families only ^[8].

The chart: five families, three widths, one mistranslation

Model	Band size	Case, as stated	Wrist fit, as stated	Listings	Label form and watch-outs
GMT Diver's 104	20mm ^[1]	Approximately 40x40x12mm ^[1]	14.5-21cm ^[1]	7 ^[5]	Printed Lug width: 20mm ^[1], label first, on every dial: white, navy, green, black, Biwa Trout Salmon, Biwa Lake Kasumi and Lake Biwa Blue, the last three named after fish and haze patterns of Lake Biwa, the lake the 200m diver is named for ^[5]. Movement is a Japanese-made "SEIKO TMI NH34A" GMT automatic ^[1], weight stated 167g. The 40x40 case figures are case dimensions, not strap dimensions.
Seiran	18mm ^[2]	Approximately 38x38x12mm ^[2]	15-20cm ^[2]	49 ^[5]	Printed Lug width: 18mm ^[2] identically on silver, blue and black dials across every strap option: oil leather, smooth leather, croc-embossed leather, Tochigi leather NATO and the 5-link steel bracelet, plus three green-dial pre-orders live at build ^[5]. Width does not change with strap option: a Seiran on steel and a Seiran on NATO take the same 18mm.
Biwa	18mm ^[3]	Approximately 38x38x12mm ^[3]	15-20cm ^[3]	12 ^[5]	Printed Lug width: 18mm ^[3] on both naming halves of the family, Biwa Trout Salmon and Lake Biwa Blue, across the same strap-option matrix as Seiran ^[5]. Same case and same width as Seiran: the families differ in dial story, not in strap size, so one 18mm strap SKU serves both.
Awazu	14mm ^[4]	Approximately 28x28x11mm cushion ^[4]	13.5-18cm ^[4]	20 ^[5]	Printed in its own word order, the width between lugs: 14mm ^[4], value before label, on black, silver, blue, Biwamasu Salmon and Lake Biwa Blue dials across silver, gold and rose-gold case metals ^[5]. The Japanese page for the same watch states lug width 14mm in the plain label order, so the two stores agree on the number ^[9]. The 28x28x11mm figures are cushion-case dimensions, not widths; nothing on this page reprints them as a strap size. 14mm is an understocked width in the strap trade, worth checking stock before ordering.
Omi	18mm, per JP store ^[6]	Approximately 35x35x9mm ^[7]	14.5-19.5cm ^[7]	6 ^[5]	The trap row. English pages print the width between lugs: 38mm ^[7], which cannot be a strap width on a 35x35mm case. The Japanese page for the same watch prints the full block, case diameter approximately 35mm, lug-to-lug 38mm, band lug width 18mm ^[6]: the English line dropped the lug-to-lug label and pasted its value into the width slot. Charted at 18mm on the Japanese spec, with the English form recorded verbatim and flagged. Gold and silver case variants, green, black, beige, blue and beige-black dials, all on Tochigi leather NATO ^[5].

The Omi 38mm trap: a mistranslation, not a width

Every Omi listing in the English store carries this spec line: Dimensions Case: Approximately 35x35x9mm (excluding lugs and crown) the width between lugs: 38mm Wrist size: Approximately 14.5-19.5cm Weight: 58g ^[7]. Read alone, it looks like a watch with a 38mm band, four sizes wider than anything else in the catalog. It cannot be: 38mm is wider than the 35mm case itself. The Japanese store sells the same six watches, and its spec block reads, in translation, case diameter approximately 35mm, case thickness approximately 8.9mm, lug-to-lug 38mm, band lug width 18mm ^[6]. The 38mm exists in the Japanese block too, one line up, as the lug-to-lug span, the tip-to-tip length of the case including the lugs. The English translation lost that line's label and fused its number into the width sentence. This chart carries Omi at 18mm and quotes both stores so the correction is auditable: buy an 18mm strap for any Omi, and treat any guide that lists Omi at 38mm as having read the English page with the dictionary switched off.

Two label vocabularies, and why the word order is the tell

The label-vocabulary census across all 94 watch pages finds exactly two width-stating forms, and they sort by case shape ^[5]. The round-case families print the label first: Lug width: 20mm on all 7 GMT listings, Lug width: 18mm on all 49 Seiran and all 12 Biwa listings. The cushion-case families print the value first: the width between lugs: 14mm on all 20 Awazu listings and the width between lugs: 38mm on all 6 Omi listings. Every page also carries the phrase (excluding lugs and crown) inside its case line, 94 of 94, which owns no width at all ^[5]. The practical tell for a reader holding one JIOS page: label-first means the number is trustworthy as printed; value-first means cross-check before buying, because that is the word order the Omi mistranslation lives in. The Awazu value-first line happens to be correct, and its Japanese sibling page confirms it, lug width 14mm ^[9]; the Omi value-first line is not, and its Japanese sibling page corrects it to 18mm ^[6].

The census: 94 watch listings, zero guessed rows

The English store's product sitemap, pulled fresh at build, carries 112 URLs ^[5]. Of those, 18 are not watches: 16 replacement-strap and strap-adjacent listings plus 2 engraving services, and they are excluded from the chart by what they are, though the strap pages co-state Dimensions Lug width: 18mm in their own spec blocks and are used below as corroboration ^[8]. The remaining 94 are watch listings, and every one of them prints a width line: 7 GMT at 20mm, 49 Seiran at 18mm, 12 Biwa at 18mm, 20 Awazu at 14mm, 6 Omi carrying the mistranslated 38mm English form resolved to 18mm by the Japanese store ^[5]^[6]. Dial and strap variants consolidate to one row per family here, with listing counts stated, because the width never varies inside a family: the 49 Seiran listings are one width, not 49 opinions. One coverage note: the Japanese store additionally sells a pair watch, the Awazu no Seiran, absent from the English sitemap at build; it shares the 28x28x11mm cushion case and splits by wrist, men's band 18mm, women's band 14mm ^[10]. It is recorded here rather than charted, because the English store this chart censuses does not carry it.

What the strap shop corroborates, and what it does not cover

JIOS sells its own replacement straps, and every strap listing in the English store is an 18mm strap. The brown smooth cowhide page states it twice: This replacement watch strap (18mm lug width) in the body copy and Dimensions Lug width: 18mm in its spec block ^[8]. That is a third independent confirmation of the 18mm family, and it covers Seiran, Biwa and Omi. It also quietly documents a gap: a store whose accessory rail stocks only 18mm cannot dress its own 20mm GMT or its own 14mm Awazu, and at build no first-party strap in either width exists in the English store ^[5]. An Awazu owner needs a 14mm two-piece strap from the general trade, and a GMT owner a 20mm, and both should note the quick-release question before ordering, since the maker's pages for the watches do not state the spring-bar type.

Why no chart existed

Nobody has consolidated this catalog, including the aggregators that consolidate everyone else's. Search at build surfaces the maker's own pages, a YouTube short on the GMT that states no lug width, and generic strap retailers; none carries a per-model width table ^[13]. watchpolice serves a brand page at /brands/jios-japanese-watches that returns 200 with 32KB of shell and zero lug-width or facet content, its /brands/jios, /brands/jios-watches and /brands/jios-watch slugs all return 404, and its brands sitemap, 950 locations, carries no JIOS entry in any spelling while carrying Seiko and Rolex as controls ^[11]. watchbands.ai's brand index lists 196 brands at build with Seiko, Rolex and Citizen present and JIOS absent by slug and by whole-word text ^[12]. The nearest third-party surface is a German microbrand retailer whose per-watch pages reprint the maker's spec blocks, Seiran 18mm and Awazu 14mm among them, corroborating but not consolidating ^[13]. The gap this page fills: all five families on one table, the mistranslation corrected with both languages quoted, and the 14mm cushion case flagged as the understocked width it is.

How we verified this

On 2 October 2026 we pulled the English store's product sitemap fresh and rendered all 94 watch listings with a browser user agent and cache-busted URLs, running the label-vocabulary census before any width parsing: the only width-stating labels anywhere in the catalog are Lug width: and the width between lugs:, in the split described above, while (excluding lugs and crown), Wrist size: and Weight: lines own no width ^[5]. The Japanese store's sitemap and per-family pages were pulled the same day to cross-language-check every family: GMT 20mm, Seiran 18mm and Awazu 14mm agree across both stores, and the Omi disagreement, English 38mm against Japanese band lug width 18mm with the 38mm present as lug-to-lug, is resolved on the Japanese side with both quotes kept ^[6]^[9]. Every quoted spec span on this page was machine-checked verbatim against the saved pulls. The incumbent walls were fired fresh at build, not inherited: watchpolice slug probes in four spellings plus the shell adjudication on the 200 page, the 950-location brands sitemap grep, the watchbands.ai index walk, and two web searches, all documented in the sources below.

Related guides

The lug width chart by brand places JIOS's 14/18/20 split beside every other brand on this site, and the master band size chart indexes them all. The Awazu is one of the few current-production watches on a 14mm lug, so the measuring guide is worth a read before ordering that width. For the lug-to-lug numbers that keep getting mistaken for widths, the Omi 38mm being this catalog's own example, see lug-to-lug, explained, and the watch database lists every charted brand by width.

Sources

JIOS (official English store), GMT Diver's 104 white dial product page, rendered spec block: Dimensions Case: Approximately 40x40x12mm (excluding lugs and crown) Wrist size: Approximately 14.5-21cm Lug width: 20mm Weight: 167g; movement line a Japanese-made "SEIKO TMI NH34A"; pulled fresh at build: jios-en.com
JIOS (official English store), Seiran silver dial, blue hands, steel bracelet product page, rendered spec block: Dimensions Case: Approximately 38x38x12mm (excluding lugs and crown) Wrist size: Approximately 15-20cm Lug width: 18mm; pulled fresh at build: jios-en.com
JIOS (official English store), Biwa Trout Salmon silver hands steel bracelet product page, rendered spec block: Dimensions Case: Approximately 38x38x12mm (excluding lugs and crown) Wrist size: Approximately 15-20cm Lug width: 18mm; pulled fresh at build: jios-en.com
JIOS (official English store), Awazu Biwamasu Salmon dial silver hands product page, rendered spec block, quoted in the maker's own word order: Dimensions Case: Approximately 28x28x11mm (excluding lugs and crown) the width between lugs: 14mm Wrist size: Approximately 13.5-18cm; pulled fresh at build: jios-en.com
JIOS (official English store), store products sitemap pulled fresh 2 October 2026: 112 URLs, 94 watch listings (GMT Diver's 104 x7 all Lug width: 20mm; Seiran x49 including 3 green pre-orders, all Lug width: 18mm; Biwa x12, all Lug width: 18mm; Awazu x20, all the width between lugs: 14mm; Omi x6, all the width between lugs: 38mm) and 18 non-watch URLs (16 replacement straps, 2 engraving services): jios-en.com
JIOS (official Japanese store), Omi silver product page, rendered spec block: case diameter approximately 35mm, case thickness approximately 8.9mm, lug-to-lug 38mm, band lug width 18mm, case: 316L stainless steel, weight approximately 58g; the source that resolves the English Omi mistranslation; pulled fresh at build: jios-jp.com
JIOS (official English store), Omi gold green dial product page, rendered spec block: Dimensions Case: Approximately 35x35x9mm (excluding lugs and crown) the width between lugs: 38mm Wrist size: Approximately 14.5-19.5cm Weight: 58g; quoted verbatim as the mistranslated form, not as a strap size; pulled fresh at build: jios-en.com
JIOS (official English store), replacement strap, brown smooth cowhide leather 18mm product page, pulled fresh at build: body states This replacement watch strap (18mm lug width) and the spec block states Dimensions Lug width: 18mm Materials Leather (genuine calf leather); every strap listing in the English store is 18mm: jios-en.com
JIOS (official Japanese store), Awazu product pages, rendered spec blocks: case approximately 28x28x11mm (excluding lugs and crown), lug width 14mm, plain label order; the Japanese GMT pages state lug width 20mm and the Japanese Seiran pages state lug width 18mm, agreeing with the English store family by family; pulled fresh at build: jios-jp.com
JIOS (official Japanese store), Awazu no Seiran pair-watch product pages, rendered spec block: case approximately 28x28x11mm (excluding lugs and crown), wrist sizes men's approximately 15-20cm and women's approximately 13.5-18cm, lug width men's 18mm and women's 14mm; absent from the English store sitemap at build, recorded as coverage, not charted: jios-jp.com
watchpolice.com at build: /brands/jios, /brands/jios-watches and /brands/jios-watch return 404; /brands/jios-japanese-watches returns 200 with approximately 32KB of shell markup, zero lug-width or facet content, absent from the brands sitemap, adjudicated a shell rather than an incumbent; the /api/sitemap-brands.xml sitemap carries 950 brand locations with zero JIOS entries in any spelling while the controls /brands/seiko and /brands/rolex return 200 with lug-width content; the root /sitemap-brands.xml path 404s, it is not the sitemap: watchpolice.com
watchbands.ai brands index at build: 209 root-relative hrefs walked to 196 unique brand slugs, controls Seiko, Rolex and Citizen present, JIOS absent by slug and by whole-word text: watchbands.ai
Method-B web searches at build, two runs: zero consolidated JIOS width charts surfaced; results are the maker's own pages, a YouTube short on the GMT Diver's 104 stating no lug width, and generic strap retailers; the nearest third-party spec surface is the German retailer japanese-microbrands.com whose per-watch pages reprint the maker's spec blocks (Seiran Lug width: 18 mm, Awazu Lug width: 14 mm), corroborating the family values without consolidating them: japanese-microbrands.com