Seiko · Prospex Land and Seiko 5 Sports, SKX series
Seiko SPB379J1 vs Seiko SSK001
12 published specifications differ between these two, and 4 are identical. Every figure below is what the manufacturer states for that reference; nothing is inferred from the other watch.
What differs
| Specification | ||
|---|---|---|
| Case | Stainless steel with super hard coating, 39.5 mm | Stainless steel, 42.5 mm |
| Diameter | 39.5 mm | 42.5 mm |
| Lug to lug | 46.4 mm | 46 mm |
| Lug width | 20 mm | 22 mm |
| Water resistance | 20 bar | 10 bar |
| Crystal | Curved sapphire crystal, anti-reflective coating on inner surface | Hardlex with magnified glass |
| Bezel | Rotating compass inner ring | Rotating bezel with 24-hour display |
| Bracelet | Cow leather band, 20 mm between the lugs | 22 mm between the lugs |
| Clasp | Three-fold clasp with push button release | Three-fold clasp with push button release, with secure lock |
| Calibre | 6R54 | 4R34 |
| Power reserve | Approximately 72 hours (3 days) | Approximately 41 hours |
| Movement notes | Precision stated as +25 to −15 seconds per day. 24-hour hand for dual time display, stop second hand function. Magnetic resistance 4,800 A/m. LumiBrite on hands and indexes. | 24-hour hand for dual time display, stop second hand function and date display. Magnetic resistance 4,800 A/m. LumiBrite on hands and indexes. Total weight 161.0 g. No daily precision figure is published for this reference. |
What is identical
Worth knowing as much as the differences: these are the specifications you cannot use to tell the two apart.
- Thickness
- 13.6 mm
- Case back
- See-through and screw case back
- Movement
- Automatic with manual winding
- Jewels
- 24
Stated for one, not the other
These rows cannot be compared, because one maker publishes the figure and the other does not. An empty cell is a gap in the manufacturer's documentation, not a gap in the watch — and not a licence to fill it in from the other column.
| Crown | Screw-down crown | not stated |
|---|
What the differences cost you
Each note below follows from the published figures in the tables above — what they mean for intake, for a listing, and for the handover. Nothing here estimates a price or a margin.
These reach different buyers
42.5 mm on the SSK001 against 39.5 mm on the SPB379J1. Diameter is a poor predictor of how a watch actually sits, but it is the field buyers filter on, so the two land in front of different people. Do not let one listing's photographs or copy stand in for the other.
Do not describe these the same way
200 metres on the SPB379J1 against 100 on the SSK001. Both are more than daily life asks for, so the number is a listing-accuracy question rather than a practical one: quote each watch its own figure, and remember that neither rating survives an unserviced case by itself.
One survives the weekend and one does not
72 hours on the SPB379J1 against 41 on the SSK001. Below about sixty hours a watch left off the wrist from Friday is stopped by Monday. Wind both fully at intake and confirm they reach the stated figure — a short reserve leaves a tired barrel nowhere to hide, and it is the kind of fault a buyer reports in week two.
Different movements to verify and to service
The SPB379J1 runs the 6R54 and the SSK001 the 4R34. Two consequences at intake: the service history that is normal for one calibre is not evidence about the other, and the calibre is the check that catches a movement swapped into the wrong case. Confirm the movement matches the reference rather than assuming it from the dial.
What to check on each
SPB379J1
- Turn the inner compass ring through a full revolution using its own crown and confirm it moves smoothly and holds position. It is driven from a second crown, so a seized ring is a crown or pinion problem rather than something you can free by hand.
- Note the water resistance is given as 20 bar, not as a diver's rating. This is a Prospex on a leather band and it should not be described in the language Seiko reserves for its dive watches.
- Check both crowns screw down. There are two penetrations of the case here and the one for the inner ring is the one owners forget to secure.
SSK001
- Grade the crystal as Hardlex, not as sapphire. Hardlex scratches where sapphire would not, and those scratches can often be polished out, so a marked crystal here is a cheap fix rather than a replacement.
- Check the magnifier over the date for lifting at its edges. It is a separate element bonded to the crystal and it can detach, which is a fault a photograph rarely shows.
- Note that Seiko publishes no daily accuracy figure for this reference. Do not borrow the +25 to −15 quoted for the 6R calibres, and say in the listing that the maker does not state one.
Sources
- Seiko official product page for reference SPB379J1 (Prospex Land, Alpinist Mechanical GMT) - Caliber Number: 6R54; Movement Type: Automatic with manual winding; Precision: +25 to -15 seconds per day; Power reserve: Approx. 72 hours(3 days); Jewels: 24; Case Material: Stainless steel (super hard coating); Case Size: Thickness:13.6mm; Diameter:39.5mm; Lug-to-lug:46.4mm; Crystal: Curved sapphire crystal; Crystal Coating: Anti-reflective coating on inner surface; LumiBrite: LumiBrite on hands and index(es); Band Material: Cow leather; Clasp: Three-fold clasp with push button release; Distance between lugs: 20; Water Resistance: 20 bar; Magnetic Resistance: 4,800 A/m; Functions: 24-hour hand (dual time display function); Stop second hand function; Features: Rotating compass inner ring; Screw-down crown; See-through & Screw case back — retrieved 2026-09-22
- Seiko official product page for reference SSK001 (Seiko 5 Sports, SKX series) - Caliber Number: 4R34; Movement Type: Automatic with manual winding; Power reserve: Approx. 41 hours; Jewels: 24; Case Material: Stainless steel; Case Size: Thickness:13.6mm; Diameter:42.5mm; Lug-to-lug:46.0mm; Crystal: Hardlex with magnified glass; LumiBrite: LumiBrite on hands and index(es); Clasp: Three-fold clasp with push button release; Distance between lugs: 22; Water Resistance: 10 bar; Magnetic Resistance: 4,800 A/m; Weight: 161.0g; Functions: 24-hour hand (dual time display function); Stop second hand function; Date display; Features: Rotating bezel (24-hour display); Three-fold clasp with secure lock; See-through & Screw case back — retrieved 2026-09-22
Not affiliated with Seiko. Specifications are read from each manufacturer's own published documentation on the dates shown and may change; the manufacturer's current documentation governs.