Pipe Threads Pooley Inc.（管道螺纹普利公司。）.pdf

Technical Information Identifying Threads Pipe Threads Pipe threads are either tapered or straight (parallel). The two styles may or may not be compatible. Refer to thread information chart on page 706. Tapered threads Tapered threads are the most common type of thread available. As the name implies, they have a slight taper. When mated together and tightened, the threads compress and may form a seal. Usually a thread sealant is required. The mating threads both hold the fitting in place and seal the connection. The most widely used pipe threads in North America are NPT (National Pipe Taper). Some confusion may result from the use of NPT, FPT, and MPT in describing threads. Both FPT and MPT are NPT threads, with FPT meaning female threads (internal) and MPT meaning male threads (external). tapered threads NPTF (Dryseal) threads are modified NPT threads, which are less likely to leak without a sealant. For a leak-free seal, we recommend using a sealant compound or PTFE tape. You can use NPTF threads with NPT threads, but youll lose some of the leak-free characteristics. Straight threads Straight (parallel) threads are used for mechanical joining. They serve one purpose - to hold a fitting in place. As a result, an O-ring (elastomer), hard metal seal or a soft seat seal is required. Straight pipe threads include NPSM (National Pipe Straight Mechanical), and NPSH (National Pipe Straight Hose) Sizing and pitches may differ from the NPT threads straight threads Less common straight threads are GHT (Garde