Trapezoidal Metric Thread Machinery's Handbook, 31st Edition
2038
P
Internal Thread
30˚ a c
R 2
R 1
Z
H 4
H 1
h 3
R 2
a c
D 4
D 1
d d 2 d
3
D 2 , d 2
External Thread
Metric Trapezoidal Thread, ISO 2904 Terminology: The term “bolt threads” is used for external screw threads, the term “nut threads” for internal screw threads. Calculation: The values given in the International standards have been calculated by using the following formulas: . H P 05 1 = . H H a P a 05 c c 4 1 = + = + . H H a P a 05 c c 3 1 = + = + D d a 2 c 4 = + . Z P H 025 2 1 = = ⁄ D d H d p 2 1 1 = − = − D D h 2 3 3 = − . d D d Z d P 2 05 2 2 = = − = − . R a R a 05 max. max. c c 1 2 = = where a c = clearance on the crest; D = major diameter for nut threads; D 2 = pitch diameter for nut threads; D 1 = minor diameter for nut threads; d = major diameter for bolt threads = nominal diameter; d 2 = pitch diameter for bolt threads; d 3 = minor diameter for bolt threads; h 1 = Height of overlapping; h 4 = height of nut threads; h 3 = height of bolt threads; and, P = pitch. Table 1. Comparison of ISO Metric Trapezoidal Screw Thread ISO 2904-1977 and Trapezoidal Metric Screw Thread DIN 103 ISO 2904 DIN 103 Comment Nominal Diameter D D S Pitch p p Same Clearances (Bolt Circle) a c b Same Clearances (Nut Circle) a c a Not same Height of Overlapping h 1 h e Same Bolt Circle h 3 = 0.50 P + a c h s = 0.50 P + a Same h as = 0.25 p z = 0.25 p Same Minor diameter for external thread D 3 = d − 2 h 3 k s = d − 2 h s Same Pitch diameter for external thread D 2 = d − 2 h as d 2 = d − 2z Same Nut Circle Basic major diameter for nut thread D 4 = d + 2 a c d n = d + a + b Not same Height of internal thread h 4 = h 3 h n = h 3 + a Not same Minor diameter of internal thread D 1 = D − 2 h 1 K n = D n − 2 h n Not same
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