Seikonaut 40mm Case – Two-Tone Gold
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- Genuine 316L Steel & Sapphire
The Two-Tone Seikonaut combines brushed silver surfaces with gold-toned accents in a dual-finish approach that mirrors the classic two-tone sports watch formula. At 9.95 mm with a solid caseback, this 40 mm case maintains the ultra-thin Nautilus-inspired profile while adding visual depth through the interplay of cool steel and warm gold. The sapphire crystal comes with clear or blue AR coating, and the screw-down crown delivers 50 m water resistance. Compatible with all NH-family movements and 30.8 mm dials, this case gives builders the two-tone aesthetic without needing two separate parts.
Specifications
| Specification | Value |
|---|---|
| Diameter | 40 mm (10H–4H) × 38 mm (12H–6H) |
| Thickness | 9.95 mm (solid caseback) / 10.3 mm (exhibition caseback) |
| Material | 316L Stainless Steel, two-tone silver and gold |
| Finish | Brushed silver with gold-toned polished accents |
| Crystal | Sapphire (clear or blue AR coating) |
| Water Resistance | 50 m |
| Dial Fit | 30.8 mm |
| Crown | Screw-down, included |
Compatibility
Movements: NH35, NH36, NH38, NH70, NH71, NH72 — all standard Seiko NH-family automatics fit without modification. The crown stem must be cut to length during installation.
Dials: 30.8 mm dials only. Gold, champagne, or silver dials complement the two-tone finish naturally. A white dial keeps things classic, while a dark blue or black dial creates a dressier contrast.
Strap/Bracelet: Compatible with the Seikonaut integrated bracelet. A two-tone bracelet or a leather strap in brown or tan can extend the dual-tone theme to the wrist. Standard spring bar attachment at the lugs.
Not compatible: 7S26 and 7S36 movements use a different stem height and are not recommended for this case.
What’s Included
- Seikonaut case body (316L steel, two-tone silver and gold finish)
- Caseback (solid or exhibition, depending on variant selected)
- Screw-down crown with signed logo
- Crystal gasket and caseback gasket
- Sapphire crystal (pre-installed, clear or blue AR coating)
Tools are not included. You will need a case opener, hand press, stem cutter, movement holder, and rodico to complete your build.
Why We Chose This Case
Two-tone watches are a defining look in luxury horology — the Patek Philippe Nautilus and Audemars Piguet Royal Oak both have iconic two-tone references. The Seikonaut two-tone translates that concept into a moddable platform: brushed silver on the broad surfaces for everyday subtlety, and gold-toned accents on the polished edges and bezel details to catch the light. The dual-tone approach is applied at the case level, so builders can pair it with matching gold hands for full cohesion or use contrasting silver hands for a more understated interpretation. The 9.95 mm ultra-thin profile keeps the proportions tight, avoiding the top-heavy look that plagues thicker two-tone mod cases.
Build Guide
Difficulty: Moderate — suitable for first-time builders with proper tools and patience.
Tools needed: Case opener (or case press), hand press or hand setting tool, stem cutter, movement holder, rodico, and tweezers.
Two-tone specific tips:
- Protect both finishes: The gold-toned accents are more visible when scratched than the brushed silver surfaces. Use rodico and plastic tweezers during assembly to keep both finishes clean.
- Stem cutting: Measure twice, cut once. Leave 0.5 mm extra and trim down gradually to avoid cutting too short.
- Gasket seating: Both gaskets must sit flat in their channels for the 50 m water resistance rating. Check alignment before pressing the caseback.
For full step-by-step instructions, see our complete Seiko mod build guide.
Frequently Asked Questions
Is the gold part real gold?
No. The gold-toned accents are a PVD coating applied over 316L stainless steel. PVD is more durable than traditional gold plating and maintains its color significantly better with daily wear. The look is gold-tone, not solid gold, which keeps the case accessible while delivering the visual two-tone effect.
What hands should I use with a two-tone case?
Gold or yellow gold hands create the most cohesive look, matching the gold accents on the case. Silver hands work well for a subtler two-tone where the gold accents on the case provide the only warm element. Our Gold V2 Nautilus Hands were designed to match this case’s gold tone.
How thin is this compared to other two-tone Nautilus cases?
At 9.95 mm (solid caseback) and 10.3 mm (exhibition), the Two-Tone Seikonaut is 2–4 mm thinner than most Nautilus-style mod cases on the market. Two-tone cases from other brands are often even thicker than their single-tone counterparts. The Seikonaut maintains the same slim profile across all finishes.
Complete Your Build
- Silver Nautilus Skeleton Dial (30.8 mm) — classic silver dial, lets the case’s gold accents stand out
- Gold V2 Nautilus Hands — match the gold accents on the case for full two-tone cohesion
- Seiko NH35 Movement — reliable workhorse movement for an everyday two-tone build
- Seiko NH72 Skeleton Movement — golden bridges complement the two-tone aesthetic through the exhibition caseback
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Nautilus-Style Seiko Mod Parts · All Seiko Mod Cases · Nautilus Seiko Mods
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