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                 412    Mechanical Engineering Design
                  Table 8–1
                                           Nominal         Coarse-Pitch Series            Fine-Pitch Series
                  Diameters and Areas of     Major             Tensile-   Minor-            Tensile-   Minor-
                                                                                             Stress
                                                               Stress
                  Coarse-Pitch and Fine-   Diameter    Pitch  Area A t   Diameter   Pitch   Area A t  Diameter
                                                        p
                                               d
                                                                                      p
                                                                                                       Area A r
                                                                         Area A r
                  Pitch Metric Threads.*      mm       mm       mm 2       mm 2      mm      mm  2      mm 2
                                               1.6     0.35       1.27       1.07
                                               2       0.40       2.07       1.79
                                               2.5     0.45       3.39       2.98
                                               3       0.5        5.03       4.47
                                               3.5     0.6        6.78       6.00
                                               4       0.7        8.78       7.75
                                               5       0.8       14.2       12.7
                                               6       1         20.1       17.9
                                               8       1.25      36.6       32.8     1         39.2       36.0
                                              10       1.5       58.0       52.3     1.25      61.2       56.3
                                              12       1.75      84.3       76.3     1.25      92.1       86.0
                                              14       2        115        104       1.5      125        116
                                              16       2        157        144       1.5      167        157
                                              20       2.5      245        225       1.5      272        259
                                              24       3        353        324       2        384        365
                                              30       3.5      561        519       2        621        596
                                              36       4        817        759       2        915        884
                                              42       4.5     1120       1050       2       1260       1230
                                              48       5       1470       1380       2       1670       1630
                                              56       5.5     2030       1910       2       2300       2250
                                              64       6       2680       2520       2       3030       2980
                                              72       6       3460       3280       2       3860       3800
                                              80       6       4340       4140       1.5     4850       4800
                                              90       6       5590       5360       2       6100       6020
                                             100       6       6990       6740       2       7560       7470
                                             110                                     2       9180       9080

                                          *The equations and data used to develop this table have been obtained from ANSI B1.1-1974 and B18.3.1-1978.
                                          The minor diameter was found from the equation d r = d −1.226 869p, and the pitch diameter from d p = d −
                                          0.649 519p. The mean of the pitch diameter and the minor diameter was used to compute the tensile-stress area.


                                              Square and Acme threads, whose profiles are shown in Fig. 8–3a and b, respec-
                                          tively, are used on screws when power is to be transmitted. Table 8–3 lists the pre-
                                          ferred pitches for inch-series Acme threads. However, other pitches can be and often
                                          are used, since the need for a standard for such threads is not great.
                                              Modifications are frequently made to both Acme and square threads. For instance,
                                          the square thread is sometimes modified by cutting the space between the teeth so as
                                          to have an included thread angle of 10 to 15 . This is not difficult, since these threads
                                                                              ◦
                                          are usually cut with a single-point tool anyhow; the modification retains most of the
                                          high efficiency inherent in square threads and makes the cutting simpler. Acme threads
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