Quote Originally Posted by Ed Sukach
I can't ever remember coming across a 25 T.P.I. thread. I wonder,

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.
Was measured with screw pitch gauges, both metric and imperial......yep I've never seen one before either.

Clayton