wju:  The Kraghaus barrel scope-mount information (that can be accessed through the classifieds on this Forum) states that Krag sight screws are reportedly 8-26 (an obsolete thread size).  They are also reported to be a rare metric size M4 (.159 " diameter and 1.0 mm pitch).  Possibly some of the Krag's thread peculiarities are related to its Norwegian origins?
  I once had a Krag sporter that had the sight holes filled with lead.  This protected the threads and was not too unsightly.  (A small lead split shot could be tapped into the hole with a copper hammer;  the excess could be shaved smooth with a sharp blade, taking care not to scatch the barrel finish).  The lead plugs stayed in place but were easily removed.