Thanks for all the off-list responses. Others also report problems with some, but not all these stems. The most likely explanation offered was that they were available both for alloy bars (presumably 26.0) and in 25.4 for steel bars. This sounds plausible, since these stems were probably most often used on the track, and steel track bars were still common in the 60's. So it would seem I should use this stem with 25.4 bars like British GB or JIS dimension Japanese bars of which Nitto still makes some very fine ones.
Regards,
Jerry Moos
Houston, TX