各种管接头标准.doc

Standard Pipe ThreadsThere are many pipe thread specifications but they fall into one of two categories: The North American or US Standard and the Rest of the world.The US has the National Standard Pipe Thread designated NPT and a variation of it, the dryseal thread designated NPTF. They are really the same thread. The dryseal thread differs in that the roots of the threads are slightly more truncated than the crests. The dryseal was designed to be sealed without thread sealant. If you are going to use thread sealant anyway, the fittings can be used interchangeably. Sometimes you will see NPTF used to designate National Pipe Thread Female and NPTM for National Pipe Thread Male. If someone tries to tell you this, insult them properly for being idiots.The rest of the world is based off of the British Standard Pipe Threads. There are tapered and straight thread versions. Sometimes you will hear them called BSPT and BSPP respectively. The British dont call their threads that. They designate them as R and R Tr respectively. Germany, France, and Japan all have their own names for the threads. They are shown in the table.The National Standard and the British Standard also differ in that their pitches or threads per inch are slightly different. If you pick up two fittings they will almost go together. Dont try to put them together though. At best, youll just ruin both fittings. Only the nominal 1/2 and 3/4 have the same pitch. Still, dont try to put them together (it may work) because the thread forms are slightly different and you may have a difficult time putting them together.Why the two thread systems are similar but not quite the same is a mystery to me. My theory (being an American) is that it was invented here and the Brits couldnt stand it so they changed it just slightly so they would never have to use an American made product. The rest of the Europeans (and Japan) couldnt stand using an English thread and further changed the name and called it metric. Im sure the