I've been lurking on these forums for over a year and during this time I haven't heard of a documented difference between the two variants, quality-wise. If I were to buy the SKX007 I would buy the 'K' version, since it's cheaper.
And here: http://www.thewatchforum.co.uk/index.php?showtopic=73423. You can also read the official response from Seiko Japan: "The watch ref.#SKX007J and SKX007K are completely same watch model. The shipping route is slightly different. We are not able to inform you of the details"
Open up a lot of "Made in Japan" Seikos, and inside it says that the case is made in (typically) China. As far as SKX's go, there's no difference apart from the writing on the dial. This doesn't apply to Grand Seikos and the like - they are made in Japan in every sense of the word.
SKX's are great watches for the money - I enjoy mine. If you like the extra text on the dial, go for the Made in Japan version - if you prefer the cleaner look, go for the K version and save a little money.
There are only 2-3 optical differences , nothing else, I believe that the letter makes deferences only to collectors .
Some people says that the j are made in Japan and k are made in Malaysia or wherever seiko has factory .
Personally I have two k since are cheaper .
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