5.2 THREADING AND THREAD SYSTEMS

Thread-turning inserts are available in different styles or types for turning external and internal thread systems such as UN series, 60 metric, Whitworth (BSW), Acme, ISO, American buttress, etc. Figure 5.6 shows some of the typical thread-cutting inserts.

The defining dimensions and forms for various thread systems are shown in Fig. 5.7a to k with indications of their normal industrial uses. The dimensions in the figure are in U.S. customary and metric systems as indicated. In all parts of the figure, P = pitch, reciprocal of threads per inch (for U.S. customary) or millimeters (for metric).

Figure 5.7a defines the ISO thread system: M (metric) and UN (unified national). Typical uses: All branches of the mechanical industries. Figure 5.7b defines the UNJ thread system (controlled-root radii). Typical uses: Aerospace industries. Figure 5.7c defines the Whitworth system (BSW). Typical uses: Fittings and pipe couplings for water, sewer, and gas lines. Presently replaced by ISO system. Figure 5.7d defines the American buttress system, 7 face. Typical uses: Machine design. Figure 5.7e defines the NPT (American national pipe thread) system. Typical uses: Pipe threads, fittings, and couplings. Figure 5.7f defines the BSPT (British standard pipe thread) system. Typical uses: Pipe thread for water, gas, and steam lines. Figure 5.7g defines the Acme thread system, 29 . Typical uses: Mechanical industries for motion-transmission screws. Figure 5.7h defines the stub Acme thread system, 29 . Typical uses: Same as Acme, but used...