22. Basic Profile of Threads Intro American Standard Taper Pipe Threads (NPT) Truncation Unit: mm Threads per inch Section fc = fr SP InternalThreads Max. 0.096PThreads per inch27Min.0.033P 18 Max.Min. 0.088P0.033P SL Max. 0.078P 14 Min. 0.033P Central axisExternal Threadsline of thread Max. 0.073P11.5Min.0.033PMax.0.062PPO 8 Min. 0.033P Dryseal American Standard Taper Pipe Threads (NPTF) Truncation Unit: mm ST Threads per inch Section fc fr InternalThreads Max. 0.094P 0.140PThreads per inch27Min.0.047P0.094PMax.0.078P0.109PROLL 18 Min. 0.047P 0.078P Max. 0.060P 0.085P 14 Min. 0.036P 0.060P Central axisExternal Threadsline of thread Max. 0.060P 0.090P11.5Min.0.040P0.060PCARBIDE Max. 0.055P 0.076P 8 Min. 0.042P 0.055P Metric Trapezoidal Screw Threads (Tr) 29˚ Trapezoidal Screw Threads (29 Tr) LONG HAND TAPS Internal Thread Internal EG (STI) Threads External Threads SPECIALTHREADS, GAUGES External Thread THREAD MILLS DIES Threads per inch CENTER DRILLS Technical info 711 d1 or D1 d2 or D2 d or D d1 D1 d2 or D2 d D