I can't ever remember coming across a 25 T.P.I. thread. I wonder,Originally Posted by claytume
1) How was the pitch determined? ... by measurement or ? If someone used the folding "Thread Pitch Gages", they might well mistake a 1 millimeter pitch for ...? Then again, I can't ever remember seeing a folding thread pitch gauge (National Thread Form) with a 25 T.P.I leaf.
2) Is it possible that the thread in question had something other than a 60 degree National/ Metric form? I don't know ... but it might have been something like a Whitworth (55 degree rounded) or Lowenhertz 53 degrees, 30 minutes; or -- or Dardelet Self-Locking ... or ..... I don't know what the "standard" pitches were for those.