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TM 9-254
4-27. Hand Tap Nomenclature - Continued
t.
Rake. Any deviation of a straight cutting face of the tooth from a radial line. Positive Rake means that the crest
of the cutting face is angularly advanced ahead of the balance of the face of the tooth. Negative Rake means that the
same point is angularly behind the balance of the cutting face of the tooth. Zero Rake means that the cutting face is
directly on the center line.
u.
Root. The bottom surface joining the flanks of two adjacent threads. The root of an external thread is at its minor
diameter, while the root of an internal thread is at its major diameter.
v.
Spiral Point (Chip Driver). A supplementary angular fluting cut in the cutting face of the land at the chamfer end.
It is slightly longer than the chamfer on the tap and of the opposite hand to that of rotation.
w.
Thread Relief. The clearance produced by removal of metal from behind the cutting edge. When the thread
angle is relieved from the heel to cutting edge, the tap is said to have "Eccentric" relief. If relieved from heel for only a
portion of land width, the tap is said to have "Con-eccentric" relief.
4-28. Thread Limits.
Table 4-10. Thread Limits, Type I, Series A Through C, Cut Thread Taps
Threads Per Inch
Major Diameter Limits
Pitch Diameter Limits
Screw Gage
Number or
Diameter
Series
A
Series
B
Series
C
Basic
Min.
Max.
Basic
Min
Max.
Inches
Inch
Inch
Inch
Inch
Inch
Inch
0...........
............
80
............
0.0600
0.0609
0.0624
0.0519
0.0521
0.0531
1...........
64
............
.............
.0730
.0740
.0755
.0629
.0631
.0641
1...........
............
72
.............
.0730
.0740
.0755
.0640
.0642
.0652
2...........
56
............
.............
.0860
.0872
.0887
.0744
.0746
.0756
2...........
............
64
.............
.0860
.0870
.0885
.0759
.0761
.0771
3...........
48
............
.............
.0990
.1003
.1018
.0855
.0857
.0867
3...........
............
56
.............
.0990
.1002
.1017
.0874
.0876
.0886
4...........
............
............
32
.1120
.1142
.1162
.0917
.0922
.0937
4...........
............
............
36
.1120
.1137
.1157
.0940
.0942
.0957
4...........
40
............
.............
.1120
.1136
.1156
.0958
.0960
.0975
4...........
............
48
.............
.1120
.1133
.1153
.0985
.0987
.1002
5...........
40
............
.............
.1250
.1266
.1286
.1088
.1090
.1105
5...........
............
44
.............
.1250
.1264
.1284
.1102
.1104
.1119
6...........
32
............
.............
.1380
.1402
.1422
.1177
.1182
.1197
6...........
............
............
36
.1380
.1397
.1417
.1200
.1202
.1217
6...........
............
40
.............
.1380
.1396
.1416
.1218
.1220
.1235
8...........
32
............
.............
.1640
.1662
.1682
.1437
.1442
.1457
8...........
............
36
.............
.1640
.1657
.1677
.1460
.1462
.1477
8...........
............
............
40
.1640
.1656
.1676
.1478
.1480
.1495
10.........
24
............
.............
.1900
.1928
.1948
.1629
.1634
.1649
10.........
............
............
30
.1900
.1923
.1943
.1684
.1689
.1704
10.........
............
32
............
.1900
.1922
.1942
.1697
.1702
.1717
12.........
24
............
............
.2160
.2188
.2208
.1889
.1894
.1909
12.........
............
28
............
.2160
.2184
.2204
.1928
.1933
.1948
12.........
............
............
32
.2160
.2182
.2202
.1957
.1962
.1977
14.........
............
............
20
.2420
.2452
.2477
.2095
.2100
.2120
4-62 Change 6
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