Seiko 5 Sports GMT SSK001 vs San Martin SN0123 GMT

Both are GMT watches in the mid tier. In short: the San Martin SN0123 GMT takes more water (200m) — both are fine for swimming, but it has more margin if you dive. The Seiko 5 Sports GMT SSK001 is automatic, 100m water resistance, 42.5mm, hardlex crystal; the San Martin SN0123 GMT is automatic, 200m water resistance, 39mm, sapphire crystal.

Last verified 2026-06-27 · specs from manufacturer data · tier = price band, confirm the live price at the retailer

Spec	Seiko 5 Sports GMT SSK001	San Martin SN0123 GMT
Movement	Automatic	Automatic
Water resistance	100m	200m
Case size	42.5mm	39mm
Crystal	hardlex	sapphire
Style	GMT / travel	GMT / travel
Price tier	Mid	Mid

Which should you buy?

The San Martin SN0123 GMT takes more water (200m) — both are fine for swimming, but it has more margin if you dive
The San Martin SN0123 GMT has a sapphire crystal — more scratch-resistant for daily wear
The Seiko 5 Sports GMT SSK001 wears 42.5mm vs the San Martin SN0123 GMT's 39mm — choose by wrist size

Where to buy

Seiko 5 Sports GMT SSK001See price on AmazonCheck price

San Martin SN0123 GMTSee price on AmazonCheck price

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FAQ

What's the difference between the Seiko 5 Sports GMT SSK001 and the San Martin SN0123 GMT?
Both are GMT watches in the mid tier. The Seiko 5 Sports GMT SSK001 is automatic, 100m water resistance, 42.5mm, hardlex crystal; the San Martin SN0123 GMT is automatic, 200m water resistance, 39mm, sapphire crystal.

Which has better water resistance, the Seiko 5 Sports GMT SSK001 or the San Martin SN0123 GMT?
The San Martin SN0123 GMT, rated 200m, versus 100m on the other. Pick 100m or higher for swimming and 200m+ for diving.

Which is better value, the Seiko 5 Sports GMT SSK001 or the San Martin SN0123 GMT?
Both sit in the mid tier, so it comes down to movement, water resistance and case size — see the spec table above.

Citing these specs? Go ahead — manufacturer data, last verified 2026-06-27. Copy a ready-made reference:

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