21. Taps for Pipe Threads ■Comparison of the thread limit of taper pipe tap Description of products ~ ~ Basic diameter position Basic diameter position ~Basic diameter position ~ ~ ~ ~ ~ ~ ~ ha : upper deviation ~ ~ ~ ha P = 25.4/n hd n = Number of threads hd : upper deviation Taper hd : lower deviation Axis of tap Unit : mm ISO (Rc) Appendix (PT) Thread Limit Basic major Number of PT Thread S-PT Thread ha hd Size Dia. of Threads Basic Diameter Basic Diameter Basic Diameter Gauge Plane Thread Length Position Thread Length Position Thread Length Position Basic Size Tolerance Basic Size Tolerance ( m) ( m) 1/ 16 ~ 1/ 8 ~ 1/ 4 ~ 3/ 8 ~ 1/ 2 ~ 3/ 4 ~ ~ 1/ 4 ~ 1/ 2 ~ ~ 1/ 2 ~ ~ ~ Information Technical Note : JIS standard has 2 types of Taper pipe thread, PT and S-PT taps. ISO standard has one type of Taper pipe thread Rc. : Threads per inch Technical-58 829