Machinery's Handbook, 31st Edition
Alternate Stub Acme Screw Threads
2077
0.02 p
0.2165 p
0.250 p
p 2
p 2
h
Pitch Diam. Allowance
1 2
30°
0.02 p
0.2165 p
0.227 p
60-Degree Stub Thread A clearance of at least 0.02 × pitch is added to depth h to produce extra depth, thus avoid ing interference with threads of mating part at minor or major diameters. Basic thread thickness at pitch line = 0.5 × pitch p ; basic depth h = 0.433 × pitch; basic width of flat at crest = 0.25 × pitch; width of flat at root of screw thread = 0.227 × pitch; basic pitch diameter = basic major diameter − 0.433 × pitch; basic minor diameter = basic major diameter − 0.866 × pitch. Square Thread.— The square thread is so named because the section is square, the depth, in the case of a screw, being equal to the width or one-half the pitch. The thread groove in a square-threaded nut is made a little greater than one-half the pitch in order to provide a slight clearance for the screw; hence, the tools used for threading square-threaded taps are a little less in width at the point than one-half the pitch. The pitch of a square thread is usually twice the pitch of an American Standard thread of corresponding diameter. The square thread has been superseded quite largely by the Acme form which has several advantages. See ACME SCREW THREADS . 10-Degree Modified Square Thread: The included angle between the sides of the thread is 10 degrees (see accompanying diagram). The angle of 10 degrees results in a thread which is the practical equivalent of a “square thread,” and yet is capable of economical pro duction. Multiple thread milling cutters and ground thread taps should not be specified for modified square threads of the larger lead angles without consulting the cutting tool manufacturer.
Clearance (See Note)
Nut
0.25 p
p
2
0.4563 p
p
h
1 2
Pitch Diameter Allowance
0.25 p
2
5˚
G
Screw
Clearance (See Note)
In the following formulas, D = basic major diameter; E = basic pitch diameter; K = basic minor diameter; p = pitch; h = basic depth of thread on screw depth when there is no clearance between root of screw and crest of thread on nut; t = basic thickness of thread at pitch line; F = basic width of flat at crest of screw thread; G = basic width of flat at root of screw thread; C = clearance between root of screw and crest of thread on nut: E = D − 0.5 p ; K = D − p ; h = 0.5 p (see Note); t = 0.5 p ; F = 0.4563 p ; G = 0.4563 p − (0.17 × C ). Note: A clearance should be added to depth h to avoid interference with threads of mating parts at minor or major diameters.
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