Seiko Mod Glossary
The key terms around Seiko mods and watch modding — from NH35 to sandwich dial.
- NH35
- Seiko (Time Module / TMI) automatic movement with hand-winding and hacking seconds. The standard movement in many Seiko mods — robust and easy to regulate.
- NH36
- Same as the NH35 but with a day-date complication instead of date only.
- Donor / Donor-Uhr
- Donor watch (e.g. Seiko SKX007 or SRPD) supplying the case or movement used in a mod.
- SKX007
- Seiko's most popular donor diver (200 m, 42 mm, discontinued). Enormous aftermarket parts ecosystem.
- SRPD (5KX)
- Current Seiko 5 Sports line, a common donor with NH36 movement and 4 o'clock crown.
- Bezel / Lünette
- The ring around the dial. On diver mods usually a uni-directional rotating bezel with an insert.
- Bezel Insert
- The insert inside the bezel (aluminium, ceramic or steel) carrying the scale — defines the look (e.g. Pepsi, Batman).
- Chapter Ring
- The inner ring between dial and crystal, often carrying the minute track. A misaligned chapter ring is a common QC complaint.
- Sapphire / Saphirglas
- Scratch-resistant crystal (9 Mohs). Replaces softer Hardlex/mineral glass on premium mods.
- Hardlex
- Seiko's hardened mineral crystal. Cheaper than sapphire but more prone to scratches.
- Double Dome / Box Sapphire
- Heavily domed sapphire crystal giving a vintage edge distortion.
- AR-Coating
- Anti-reflective coating on the crystal for better legibility.
- Sandwich Dial
- Two-layer dial where lume sits beneath cut-out indices for a deeper look.
- Lume / Leuchtmasse
- Photoluminescent coating (usually Super-LumiNova or BGW9) on indices and hands.
- Lollipop / Lollipop-Sekunde
- Seconds hand with a round lume dot near the tip — typical of many diver mods.
- Cyclops
- Magnifier over the date window (Datejust/GMT style).
- Jubilee-Band
- Five-link stainless steel bracelet in the Datejust style.
- Oyster-Band
- Three-link sporty stainless steel bracelet.
- President-Band
- Three-link semicircular bracelet in the Day-Date style.
- Endlinks
- Connector pieces between bracelet and case. Solid endlinks fit more tightly than hollow ones.
- Lug Width / Bandanstoß
- Distance between the lugs in mm (often 20 mm), determining strap width.
- Crown / Krone
- Control for winding and setting. 'Screw-down' means it screws in for water resistance.
- Caseback / Gehäuseboden
- Back of the case, screwed or pressed in; often engraved or fitted with a display window.
- Crystal Gasket
- Sealing ring between crystal and case.
- Movement Holder / Spacer
- Ring that secures the movement inside the case.
- Day-Date
- Display of weekday and date (NH36).
- GMT
- Extra 24-hour hand for a second time zone. Note: NH35 'GMT' mods are usually cosmetic, not a true mechanical GMT.
- Tachymeter
- Bezel scale for measuring speed (Daytona/chronograph style).
- Regulierung / Regulation
- Fine-tuning the movement's accuracy (often targeting ±10 s/day or better).
- Hacking
- Seconds-stop when the crown is pulled — allows setting to the exact second.
- Power Reserve / Gangreserve
- Running time when fully wound; about 41 hours on the NH35.
- Water Resistance / Wasserdichtigkeit
- Rated in m or ATM. Can drop after a mod if gaskets/crystal are not seated correctly.
- 316L Edelstahl
- Corrosion-resistant surgical-grade steel, standard for premium mod cases and bracelets.
- PVD / DLC
- Coating processes for dark/coloured, scratch-resistant finishes.
- Homage / Hommage
- A watch that references a classic design without copying logos or trademarks.
- Franken / Frankenwatch
- A mod assembled from mixed-source parts — pejorative for sloppy builds, neutral for custom ones.
- Aftermarket
- Third-party (non-OEM) parts used for mods.
- Built to order
- Individually assembled per order rather than shipped from stock.
- QC (Quality Control)
- Quality control: checking alignment, timekeeping, sealing and finishing before shipping.
- Insert-Stil: Pepsi / Batman / Coke
- Common two-tone GMT bezels: Pepsi (blue-red), Batman (blue-black), Coke (red-black).
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