Machinery's Handbook, 31st Edition
2084
BUTTRESS THREADS Table 5. American National Standard External Thread Allowances for Classes 2 and 3 Buttress Inch Screw Threads ANSI/ASME B1.9-1973 (R2017)
Basic Major Diameter, Inch
From 0.5 thru 0.7
Over 0.7 thru 1.0
Over 1.0 thru 1.5
Over 1.5 thru 2.5
Over 2.5 thru 4
Over 4 thru 6
Over 6 thru 10
Over 10 thru 16
Over 16 thru 24
Threads per Inch
Pitch, p Inch
Allowance on Major, Minor and Pitch Diameters of External Thread, Inch
20 16 12 10
0.0500 .0037
....
....
....
....
.... ....
.... .... ....
.... .... ....
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0.0625 .0040 .0042 .0043 .0046 .0049
0.0833 .0044 .0046 .0048 .0050 .0053 .0056
0.1000 0.1250 0.1667 0.2000 0.2500 0.3333 0.4000 0.5000 0.6667
.... .... .... .... .... .... .... .... .... .... ....
.0049 .0051 .0053 .0056 .0059 .0063 .0068
8 6 5 4 3
.... .... .... .... .... .... .... .... .... ....
.0055 .0058 .0061 .0064 .0067 .0072 .0077 .0061 .0064 .0067 .0070 .0074 .0078 .0083
.... .... .... .... .... .... .... ....
.0068 .0071 .0074 .0078 .0083 .0088 .0074 .0077 .0080 .0084 .0089 .0094
.... .... .... .... .... ....
.... .... .... .... .... ....
.0089 .0093 .0098 .0103
2.5 2.0 1.5
.... .... .... .... ....
.0100 .0104 .0109 .0108 .0113 .0118
.... .... ....
.0126 .0130 .0135 .0139
1.25 0.8000
1.0 .0152 Example Showing Dimensions for a Typical Buttress Thread.— The dimensions for a 2-inch diameter, 4 threads per inch, Class 2 buttress thread with flank angles of 7 degrees and 45 degrees are h = basic thread height = 0.1500 (Table 2) h s = h n = height of thread in external and internal threads = 0.1657 ( Table 2) 1.0000 .... G = pitch-diameter allowance on external thread = 0.0074 (Table 5) Tolerance on PD of external and internal threads = 0.0112 ( Table 4) Tolerance on major diameter of external thread and minor diameter of internal thread = 0.0112 (Table 4) Internal Thread: Basic Major Diameter: D = 2.0000 Min. Major Diameter: D − 2 h + 2 h n = 2.0314 (see Table 2) Min. Pitch Diameter: D − h = 1.8500 (see Table 2) Max. Pitch Diameter: D − h + PD Tolerance = 1.8612 (see Table 4) Min. Minor Diameter: D − 2 h = 1.7000 (see Table 2) Max. Minor Diameter: D − 2 h + Minor Diameter Tolerance = 1.7112 (see Table 4) External Thread: Max. Major Diameter: D − G = 1.9926 (see Table 5) Min. Major Diameter: D − G − Major Diameter Tolerance = 1.9814 (see Table 4 and Table 5) Max. Pitch Diameter: D − h − G = 1.8426 (see Table 2 and Table 5) Min. Pitch Diameter: D − h − G − PD Tolerance = 1.8314 (see Table 4) Max. Minor Diameter: D − G − 2 h s = 1.6612 (see Table 2 and Table 5) Buttress Thread Designations.— When only the designation, BUTT is used, the thread is “pull” type buttress (external thread pulls) with the clearance flank leading and the 7-de - gree pressure flank following. When the designation, PUSH-BUTT is used, the thread is a push type buttress (external thread pushes) with the 7-degree load flank leading and the 45-degree clearance flank following. Whenever possible this description should be
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