Threads and Threading - Sportpilot.info

1850 ANSI BUTTRESS THREADS
Löwenherz Thread
Diameter
Approximate Diameter
Pitch, No. of Threads
Millimeters Inches Millimeters per Inch Millimeters Inches
Pitch,
Millimeters
American National Standard Buttress Inch Screw Threads
Approximate
No. of Threads
per Inch
1.0 0.0394 0.25 101.6 9.0 0.3543 1.30 19.5
1.2 0.0472 0.25 101.6 10.0 0.3937 1.40 18.1
1.4 0.0551 0.30 84.7 12.0 0.4724 1.60 15.9
1.7 0.0669 0.35 72.6 14.0 0.5512 1.80 14.1
2.0 0.0787 0.40 63.5 16.0 0.6299 2.00 12.7
2.3 0.0905 0.40 63.5 18.0 0.7087 2.20 11.5
2.6 0.1024 0.45 56.4 20.0 0.7874 2.40 10.6
3.0 0.1181 0.50 50.8 22.0 0.8661 2.80 9.1
3.5 0.1378 0.60 42.3 24.0 0.9450 2.80 9.1
4.0 0.1575 0.70 36.3 26.0 1.0236 3.20 7.9
4.5 0.1772 0.75 33.9 28.0 1.1024 3.20 7.9
5.0 0.1968 0.80 31.7 30.0 1.1811 3.60 7.1
5.5 0.2165 0.90 28.2 32.0 1.2599 3.60 7.1
6.0 0.2362 1.00 25.4 36.0 1.4173 4.00 6.4
7.0 0.2756 1.10 23.1 40.0 1.5748 4.40 5.7
8.0 0.3150 1.20 21.1 … … … …
The buttress form of thread has certain advantages in applications involving exceptionally
high stresses along the thread axis in one direction only. As the thrust side (load flank)
of the standard buttress thread is made very nearly perpendicular to the thread axis, the
radial component of the thrust is reduced to a minimum. On account of the small radial
thrust, the buttress form of thread is particularly applicable when tubular members are
screwed together. Examples of actual applications are the breech assemblies of large guns,
airplane propeller hubs, and columns for hydraulic presses.
7°/45° Buttress Thread Form.—In selecting the form of thread recommended as standard,
ANSI B1.9-1973 (R1992), manufacture by milling, grinding, rolling, or other suitable
means, has been taken into consideration. All dimensions are in inches.
Form of Thread: The form of the buttress thread is shown in the accompanying Figs. 2a
and 2b, and has the following characteristics:
a) A load flank angle, measured in an axial plane, of 7 degrees from the normal to the axis.
b) A clearance flank angle, measured in an axial plane, of 45 degrees from the normal to
the axis.
c) Equal truncations at the crests of the external and internal threads such that the basic
height of thread engagement (assuming no allowance) is equal to 0.6 of the pitch
d) Equal radii, at the roots of the external and internal basic thread forms tangential to the
load flank and the clearance flank. (There is, in practice, almost no chance that the thread
forms will be achieved strictly as basically specified, that is, as true radii.) When specified,
equal flat roots of the external and internal thread may be supplied.
Table 1. American National Standard Diameter—Pitch Combinations for 7°/45°
Buttress Threads ANSI B1.9-1973 (R1992)
Preferred Nominal
Major Diameters, Inches
Machinery's Handbook 27th Edition
Threads per
Inch a
Preferred Nominal
Major Diameters, Inches
Threads per
Inch a
0.5, 0.625, 0.75 (20, 16, 12) 4.5, 5, 5.5, 6 12, 10, 8, (6, 5, 4), 3
0.875, 1.0 (16, 12, 10) 7, 8, 9, 10 10, 8, 6, (5, 4, 3), 2.5, 2
1.25, 1.375, 1.5 16, (12, 10, 8), 6 11, 12, 14, 16 10, 8, 6, 5, (4, 3, 2.5), 2, 1.5, 1.25
1.75, 2, 2.25, 2.5 16, 12, (10, 8, 6), 5, 4 18, 20, 22, 24 8, 6, 5, 4, (3, 2.5, 2), 1.5, 1.25, 1
2.75, 3, 3.5, 4 16, 12, 10, (8, 6, 5), 4
a Preferred threads per inch are in parentheses.
Copyright 2004, Industrial Press, Inc., New York, NY