NPT,PT,G, are all pipe threads,Stainless metal conduit thread head has various types,many people are not so familiar with them,so let’s say something about these threads.  NPT is abbreviation of National (American) Pipe Thread It is American taper pipe thread,it is used for sealing .it belongs to American standard’s 60 0 taping pipe thread,it is used for north America area.We can check the standard GB/T 12716-1991.PT is abbreviation for Pipe Thread,it’s taper pipe thread sealed at 55 degrees,it belongs to Wyeth thread family ,mostly be used in European and British commonwealth of nations.It usually be used in water and gas pipe industry,taper proportion is 1:16.Standard can be  referred to GB/T7306-2000

G is 55 ⁰  unthreaded sealing pipe thread, it belongs to Wyeth family,marked as G represented as straight thread.Standard can be referred to GB/T7307-2001 .G is general name of pipe thread.(Guan),55⁰, 60^{0 is    is}nctional division.That is thread is machined by a cylinder.Pipe threads are mainly used for pipe connecting.Their inner and outer thread are cooperated closely.They includes straight thread and tapering thread. Norminal diameter means the pipe diameter which connects,obviously the thread diameter is bigger than the norminal diameter.