What an NH34 build needs
| Part | What the sources say | Status |
|---|---|---|
| Movement | NH34: 24-hour hand plus hour, minute, second and date; TMI lists 243 jewels and a 5.32 mm4 height. Seiko's own version is the 4R34. | Known |
| 24-hour hand | Bore 2.2 mm in TMI's drawing1; a seller gives 2.42 mm as the hand's largest outer size.2 A seller sells an NH34/4R34 GMT hand for the SSK references.5 | Bore known; length and lume not in a maker document |
| Dial | Centre hole 2.88 mm in TMI's drawing, 2.7 mm on a seller's GMT dials; a 24-hour scale printed on the dial. Standard diameter 28.5 mm, practical thickness limit 0.6 mm (seller figures). | Hole differs by source; ask the dial maker |
| Case | Movement installed 7.99 mm high against 7.59 mm for the NH35 (seller). The SSK001 is Seiko's own case for the 4R34. | Inside depth of any case not in our data |
NH34 vs NH35
| Figure | NH34 | NH35 |
|---|---|---|
| Hands | Hour, minute, second and a 24-hour hand, plus date | Hour, minute, second and date |
| Hand bores | hour 1.5 · minute 0.88 · second 0.198 · gmt 2.2 mm1 | hour 1.5 · minute 0.88 · second 0.198 mm6 |
| Dial centre hole | 2.88 mm1 Sources disagree: manufacturer 2.88 mm / seller listing 2.7 mm2 | 2.05 mm6 |
| Installed height (seller) | 7.99 mm2seller listing | 7.59 mm2seller listing |
| Date window drawn (3 o’clock) | 2.9 × 2 mm1 | 2.9 × 2 mm6 |
| Dial feet and stem | Stem 0351 2001; feet as drawn | Stem 0351 20013; the same feet |
| Rated accuracy | not published | −20 to +40 s/day14 |
| Power reserve | not published | 41 h14 |
| Do not set the date | 21:00–04:0012 | 21:00–04:0012 |
The GMT hand and the four-hand stack
The NH34 has a fourth hand on its own shaft: a 24-hour hand beside the hour, minute and second hands. TMI's hand-fitting page draws four fitting heights for the standard type: the 24-hour wheel 0.6 mm, the hour wheel 0.818 mm, the cannon pinion 0.61 mm and the fourth wheel 0.42 mm.1 The NH35's hour wheel stands 0.88 mm, so the hour-wheel height differs by 0.062 mm between the two. Only the standard type is drawn for the NH34; the NH35 also has a high type.
The 24-hour hand bore is 2.2 mm against 1.5 mm for the hour hand. A seller says the other hands are shared across the NH family and only the dial and the 24-hour hand are GMT-specific2; the different hour-wheel height in the drawing is a reason to dry-fit rather than assume.
Dials
A dial for the NH34 needs a larger centre hole than an NH35 dial. TMI draws 2.88 mm for the NH34 and 2.05 mm for the NH351; a seller says it builds its GMT dials to 2.7 mm and that a standard dial will not fit an NH34.2 The two figures for the NH34 are different, so take the dial maker's statement that the dial is cut for the NH34, not the number alone. A second seller's GMT dial lists the NH35, NH34, 4R35 and 4R34 among its movements, in the standard 28.5 mm size.7
The date window is the same as the NH35's (2.9 × 2 mm), so a date aperture is not the problem. A GMT dial on an NH35 is possible; the larger hole shows part of the movement.2
Cases and the SSK001
Seiko's SSK001 is the stock GMT example: a Seiko 5 Sports with a 4R34 and a rotating 24-hour bezel.
Seiko SSK001, from Seiko’s own product page
Sold parts that name the SSK references in our catalogue, with the seller's own conditions:
| Part | Type | Seller says it fits | Conditions | Seller page |
|---|---|---|---|---|
| SKX007/SRPD/SSK GMT Double Dome Sapphire Crystal for flat bezel inserts - CT037F | Crystal · CT037F | Conditional: SSK001, SSK003, SSK005 | Reuse the original SSK gasket; the seller says the SKX007 crystal gasket is not compatible. | Crystaltimes9 |
| SKX007/SRPD/SSK GMT Double Dome Sapphire Crystal for sloping bezel inserts - CT037CIS | Crystal · CT037CIS | Conditional: SSK001, SSK003, SSK005 | Reuse the original SSK gasket; the seller says the SKX007 crystal gasket is not compatible. | Crystaltimes15 |
| Seiko 5 Sports SRPD 5KX SSK GMT Crystal Gasket - CT419 | Gasket · CT419 | SSK001, SSK003, SSK005 | None stated | Crystaltimes16 |
| NH34 4R34 GMT Hand - Orange - CT8120 | Hands · CT8120 | SSK001, SSK003, SSK005 | None stated | Crystaltimes5 |
| SSK Slim Caseback: Brushed Finish | Case part | Conditional: SSK001, SSK003, SSK005 | Only with a stock 4R34 movement; the seller's compatibility line requires it. Confirm the movement before buying. | namokiMODS17 |
NH34 or 4R34?
A seller of the 4R34 says it is Seiko branded and the NH34 is not, that the 4R34 is assembled in Japan and the NH34 in Malaysia, and that the rotor and some parts differ.10 TMI lists Japan or Malaysia for the NH34 (Japan or Malaysia3). Seiko rates the 4R34 at −35 to +45 s/day11 with 41 h11 of reserve and a date-change window of 21:00–03:0011; TMI prints neither accuracy nor power reserve for the NH34, and its date window is 21:00–04:0012. Treat them as two parts with a shared layout, not as one.
What is still unknown
- Inside depth and movement-holder dimensions of the SSK001 and of any mod case, so whether the extra 0.4 mm fits.
- Which centre hole an NH34 dial needs: 2.88 mm in TMI's drawing, 2.7 mm at one seller.
- NH34 accuracy, power reserve and lift angle: TMI prints them for the NH35 only.
- Length, lume and bore of aftermarket 24-hour hands beyond the seller's listing.
- Fit claims for the SSK003, SSK005 and later GMT references beyond the rows above.