Machinery's Handbook, 31st Edition
1948 Unified Screw Threads UN Internal Screw Thread: In practice it is necessary to provide for some threading tool crest wear, therefore the root of the Design Profile is rounded and cleared beyond the 0.125 P flat width of the Basic Profile. There is no internal UNR screw thread. American National Standard Unified Internal and External Screw Thread Design Profiles (Maximum Material Condition)
0.125 H
0.125 P
Rounded crest optional
60 deg 30 deg
0.5 P
0.375 H
0.625 H
Pitch line
H
0.25 P
P
0.25 H
0.25 H
Rounded root optional Nominal flat root design minor diameter
Flanks to be straight beyond 0.25 H from sharp apex of root
90 deg
Axis of external thread
0.125 H
0.125 P
Rounded crest optional
60 deg
0.5 P
0.375 H
30 deg
0.625 H
Pitch line
H
0.25 P
0.1875 H 0.6875 H
P
0.25 H
0.25 H 0.0625 H
r = 0.108 P
Tangency flank/root rad.
Flanks to be straight beyond 0.25 H from sharp apex of root Axis of external thread
UNR design minor diameter specified in dimensional tables
90 deg
UN Internal Thread (Nut) 0.125 H
Min major diameter specified in dimensional tables
0.125 P
0.375 H 0.25 H 0.25 H 0.125 H
0.25 P
0.5 P Pitch line
H
60 °
0.625 H
0.25 H
P
90 deg
Axis of internal thread ( H = height of sharp V-thread = 0.86603 × pitch)
Thread Series.— Thread series are groups of diameter-pitch combinations distinguished from each other by the numbers of threads per inch applied to a specific diameter. The various diameter-pitch combinations of eleven standard series are shown in Table 2. The limits of size of threads in the eleven standard series together with certain selected combi - nations of diameter and pitch, as well as the symbols for designating the various threads, are given in Table 3. (Text continues on page 1978)
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