[M] Metric [ST] Self-Tapping Cutting/Locking Thread [Wood] Wood Screw Thread [NPT] American National Standard Taper Pipe Thread [NPS] American National Standard Straight Pipe Thread [R] [Rc] [Rp] [R1] 55°Pipe Threads where Pressure-Tight Joints are made on the threads [G] 55°Pipe Threads where Pressure-Tight Joints are not made on the threads [Tr] Trapezoidal Thread