Threads and Threading - Sportpilot.info

1808 TRAPEZOIDAL METRIC THREADS
Z
h 3
d d 2 d 3
Machinery's Handbook 27th Edition
R 1
R 2
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 value given in the International standards have been calculated by
using the following formulas:
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 = 0.50P + a c h s = 0.50P + a Same
h as = 0.25p z = 0.25p Same
Minor diameter for external thread D 3 = d − 2h 3 k s = d − 2h s Same
Pitch diameter for external thread D 2 = d − 2h as d 2 = d − 2z Same
Nut Circle
Basic major diameter for nut thread D 4 = d + 2a 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 − 2h 1 K n = D n− 2h n Not same
P
30˚
a c
H 1
a c
External Thread
Internal Thread
R 2
H 4
D 1
D 2 , d 2
H1 = 0.5P H4 = H1 + ac = 0.5P+ ac H3 = H1 + ac = 0.5P+ ac D4 = d + 2ac Z = 0.25P = H1⁄ 2
D1 = d – 2H1 = d– p
D3 = D – 2h3 d2 = D2 = d – 2Z = d – 0.5P R1max. = 0.5ac R2max. = ac Copyright 2004, Industrial Press, Inc., New York, NY
D 4