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NPTR -National Pipe Taper Railing

This thread is used on stair banister railings and similar mechanical applications.  Care must be taken not to confuse this thread with one intended to perform a hydraulic sealing function.  While it may well work, its reliability will be compromised by a lack of thread engagement.  The basic diameter and pitch matches up across the board with NPT, but the male threads are cut short on the small end of the taper.  This shortened thread is readily noticeable to the trained eye, but could go unnoticed by the less experienced fitter.  The female fittings (typically a stanchion with a globe-shaped threaded receiver) have a clearance cut at the start of the thread to allow the male pipe thread to "disappear" when fully engaged.

NPTR Data Table alt