Less Frequently Used Thread Series and Their Uses

Most people involved in threading are familiar with the common thread symbols: NC, NF, NEF and NPT. But what about the less commonly known NPSH, NPTR and NGO?

• NPSH: This thread Used for hose couplings and nozzles and is identified as American National Straight Pipe Thread for Hose Couplings. This thread is commonly referred to as the Fire Hose Thread. A companion to this thread is IPT which is the same size in an iron pipe fitting. GHT is designate in only one size 3/4” and is not compatible with any other thread. The only application in this designation is a Garden hose.
• NPTR:  Steel railings, in practically every case, have a coupling with Railing Joint Taper Pipe Threads. These joints require a rigid mechanical thread joint with external and internal taper threads. The external thread is the same as an NPT thread except sizes ½” through 4” are shortened by 3 or 4 threads to permit the use of the larger end of the pipe thread for a more rigid connection.
• BSPP and BSPT: Both are designations for British Standard Pipe, Parallel and Taper. These pipe threads are used in many countries other than the United States where NPT and NPS are the standards.  Not only does the British Standard have a different pitch in most sizes but BSP threads have a 55º included angle rather than 60º and have radii on the crest and root of the thread. This is commonly referred to as a Whitworth form and taps are available in both full form and modified style. Modified Whitworth taps have been truncated with a flat crest and root with corner radius. The thread produced will gage properly with full form gages.
• NGO and NGT: These are gas cylinder valve threads. Valve outlet threads of various types are used to prevent accidental connection to equipment that might create a hazard. Straight threads for valve outlets are designated NGO and have American National thread form. Tapered threads are designated NGT National Gas Taper and are similar to American Standard Pipe except in length.

The engineering staff at Regal Cutting Tools can assist in applications where taps and gages are required for these important thread forms and can guide you through the tool selection process.