Seikonaut 40mm Case – Gunmetal
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- Genuine 316L Steel & Sapphire
The Gun Metal Seikonaut sits between the silver and black finishes with a dark gray PVD coating that reads industrial and modern. At 9.95 mm with a solid caseback, this 40 mm case uses the same ultra-thin Nautilus-inspired architecture as the rest of the Seikonaut line, finished in 20-micron gun metal plating over 316L stainless steel. The sapphire crystal comes with clear or blue AR coating, the screw-down crown delivers 50 m water resistance, and the case accepts all NH-family movements with 30.8 mm dials. Gun metal is the most versatile PVD finish in the lineup — it pairs well with almost any dial color and hand set.
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 with 20-micron gun metal PVD |
| Finish | Brushed and polished gun metal |
| 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. Gun metal is the most neutral dark finish in the Seikonaut range — it pairs well with silver, white, blue, green, black, and even gold-toned dials without clashing.
Strap/Bracelet: Compatible with the Seikonaut integrated bracelet. 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, 20-micron gun metal PVD)
- 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
Gun metal fills a gap in the Seikonaut lineup. Silver is classic, black is stealth, rose gold is warm — but gun metal is the chameleon. Its dark gray tone shifts depending on the light: cooler and darker indoors, warmer and more metallic in direct sunlight. This makes it the easiest finish to pair with different dial and hand combinations. The 20-micron PVD coating is applied via Physical Vapor Deposition for molecular-level adhesion, providing scratch resistance that outperforms standard plating. At 9.95 mm thick, the ultra-thin profile remains consistent across the entire Seikonaut family, regardless of finish.
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.
Common mistakes to avoid:
- Stem cutting: Cut the crown stem too short and the crown will not engage the movement. Measure twice before cutting, and leave 0.5 mm extra to trim down.
- Gasket placement: Both the crystal gasket and caseback gasket must be seated flat in their channels. A twisted gasket will compromise water resistance.
- Protecting the finish: Gun metal PVD shows scratches less than black PVD but more than bare steel. Use rodico and plastic tweezers during assembly to keep the case exterior clean.
For full step-by-step instructions, see our complete Seiko mod build guide.
Frequently Asked Questions
What is gun metal PVD?
Gun metal PVD is a dark gray coating applied to the stainless steel case via Physical Vapor Deposition. The process bonds the coating at a molecular level, making it harder and more durable than traditional plating. The gun metal shade sits between silver and black — darker than natural steel but lighter and warmer than black PVD.
What dial colors pair best with gun metal?
Gun metal is the most versatile finish in the Seikonaut range. It pairs well with nearly every dial color: silver and white for classic contrast, blue and green for a modern sport look, black for a monochromatic build, and even gold-toned dials for an unexpected warm-cool combination. This neutrality makes gun metal a popular choice for modders who plan multiple dial swaps.
How thin is the Gun Metal Seikonaut compared to other Nautilus cases?
At 9.95 mm with a solid caseback and 10.3 mm with exhibition, the Gun Metal Seikonaut is 2–4 mm thinner than most Nautilus-style mod cases, which typically sit between 12 mm and 14 mm. The slimmer profile feels more refined on the wrist and captures the proportions of the original Nautilus design more faithfully.
Complete Your Build
- Silver Nautilus Skeleton Dial (30.8 mm) — classic silver-on-gray contrast
- Silver V2 Nautilus Hands — bright hands for strong legibility against gun metal
- Seiko NH35 Movement — the standard choice for a reliable daily-wear build
- Seiko NH72 Skeleton Movement — pair with exhibition caseback for a skeleton gun metal build
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Nautilus-Style Seiko Mod Parts · All Seiko Mod Cases · Nautilus Seiko Mods
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