Seiko · Astron and Seiko 5 Sports, SKX series

Seiko SSH151J1 vs Seiko SSK001

14 published specifications differ between these two, and 1 are identical. Every figure below is what the manufacturer states for that reference; nothing is inferred from the other watch.

What differs

Specification	Seiko Astron GPS Solar 5X83, titanium with ceramic bezelSSH151J1	Seiko 5 Sports SKX series GMT, 4R34, HardlexSSK001
Case	Titanium with ceramic and titanium bezel, 43.3 mm	Stainless steel, 42.5 mm
Diameter	43.3 mm	42.5 mm
Thickness	13.4 mm	13.6 mm
Lug to lug	49.5 mm	46 mm
Crystal	Dual-curved sapphire crystal, super-clear coating	Hardlex with magnified glass
Bezel	Ceramic and titanium	Rotating bezel with 24-hour display
Case back	Screw case back	See-through and screw case back
Bracelet	Titanium; Seiko publishes a distance between lugs of 14 mm for this reference, which does not sit easily with the 43.3 mm case and should be measured before ordering parts	22 mm between the lugs
Clasp	Easy-adjust three-fold clasp with push button release	Three-fold clasp with push button release, with secure lock
Calibre	5X83	4R34
Movement	GPS solar	Automatic with manual winding
Power reserve	Operating for approximately 6 months when fully charged; power save approximately 2 years	Approximately 41 hours
Jewels	14	24
Movement notes	Precision stated as ±15 seconds per month without receiving a GPS signal, at temperatures between 5°C and 35°C. Perpetual calendar to 28 February 2100, world time for 38 cities, dual time, chronograph to 12 hours in 1/20 second increments, power reserve indicator, DST, in-flight mode, automatic hand position alignment. Listed as allergy-safe metal. Magnetic resistance 4,800 A/m. Total weight 117.0 g.	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.

Water resistance: 10 bar

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.

Lug width	not stated	22 mm

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.

One of these is the harder fit

Lug to lug is 49.5 mm on the SSH151J1 against 46 mm on the SSK001 — a 3.5 mm difference across the wrist. Diameter is what buyers ask about; lug to lug is what decides whether a case sits flat or overhangs. Ask for a wrist measurement before shipping the SSH151J1, and put the figure in the listing rather than the diameter alone.

Two different ownership conversations

The SSH151J1 is solar and the SSK001 is self-winding. That changes what a buyer needs telling at handover, and it changes intake: a hand-wound watch has no rotor to mask a tired mainspring, and a stopped quartz watch is usually a battery rather than a fault.

Different case materials, different handling

The SSH151J1 is titanium and the SSK001 is steel. Different case materials mark, polish and refinish differently, so the condition language that fits one will mislead on the other. Photograph and describe each on its own terms.

Different movements to verify and to service

The SSH151J1 runs the 5X83 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

SSH151J1

Charge it in daylight and then trigger a GPS reception before you judge anything. A solar watch that has sat in a drawer or a dark safe will behave badly until it has been charged, and that is not a fault.
Run the automatic hand position alignment function. Hands that have drifted out of alignment make every other function read wrong, and the watch has a routine to correct it.
Confirm the in-flight mode can be entered and cleared. It suppresses GPS reception, and a watch left in it will appear to have lost its ability to find a signal.

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

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.