Weston:  The shank on the issue Krag sideplate screw is about 5/16" long.  The Redfield replacement screw shank is about 7/16" long.  I believe the threads are 26 per inch.  If you got the Redfield #102 sight for a good price, I would keep it and find a machinist or gunsmith who will make you a few screws.  (Overall length including the head of the Redfield screw is 9/16").

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