Technical Production dataInformation d1 or D1 d2 or D2 d or D d1 D1 d2 or D2 d D 29. Basic pro le of threads ■American Standard Taper Pipe Threads (NPT) Truncation Unit : mm Threadsper inch Section fc=fr Internal Thread Central axis External Thread line of thread ■Dryseal American Standard Taper Pipe Threads (NPTF) Truncation Unit : mm Threadsper inch Section fc fr Internal Thread Central axis External Thread line of thread ■Metric Trapezoidal Screw Threads (Tr) ■29˚ Trapezoidal Screw Threads (TW) Internal Thread Internal Thread External Thread External Thread Technical-93