Somebody once mentioned a thread about this screw-count variation, but I have never located it. I think it would have been active about three years ago, maybe just before I joined the forum.

I was told that the two different sights are distinguished as one-screw and two-screw sights based on the screw count at the rear of the fixture. The front screw is taken for granted as they all have it.

About a year ago I was told that my K-22 OD with the serial number 646390 was the lowest numbered two-screw gun known. Looks like 638xxx just took over that distinction, and if xxx in the other serial number represents a lower number, I just got bumped back to third position.

EDITED TO ADD: Or did I misunderstand what you wrote? Is 638xxx your gun with the single-screw sight?

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David Wilson