Machinery's Handbook, 31st Edition
MEASURING SCREW THREADS 2129 the lead angle causes a wire of given size to rest higher in the groove of a thread having a small thread angle A (like a 29-degree thread) than in the groove of a thread with a larger angle (like a 60-degree American Standard). Acme Threads: Three-wire measurements of high accuracy require the use of Formula (4). For most measurements, however, Formula (2) or (3) gives satisfactory results. The table on page 2135 lists suitable wire sizes for use in Formulas (2) and (4). Values of Constants Used in Formulas for Measuring Pitch Diameters of Screws by the Three-wire System No. of
American Standard Unified and Sharp V-Thread 0.866025 P
American Standard Unified and Sharp V-Thread 0.866025 P
Whitworth Thread 0.9605 P 0.42689 0.40442 0.38420
No. of Threads per Inch
Whitworth Thread 0.9605 P 0.05336 0.04803 0.04366
Threads per Inch
0.38490 0.36464 0.34641 0.32992 0.31492 0.30123 0.28868 0.26647 0.24744 0.21651 0.19245 0.17321 0.15746 0.14434 0.12372 0.10825 0.09623 0.08660 0.07873 0.07217 0.06662 0.06186 0.05774 0.05413
18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 56 60 64 68 72 80
0.04811 0.04330 0.03936 0.03608 0.03331 0.03093 0.02887 0.02706 0.02547 0.02406 0.02279 0.02165 0.02062 0.01968 0.01883 0.01804 0.01732 0.01665 0.01546 0.01443 0.01353 0.01274 0.01203 0.01083
2 1 ∕ 4 2 3 ∕ 8 2 1 ∕ 2 2 5 ∕ 8 2 3 ∕ 4 2 7 ∕ 8 3 1 ∕ 4 3 1 ∕ 2 3
0.36590 0.34927 0.33409 0.32017 0.29554 0.27443 0.24013 0.21344 0.19210 0.17464 0.16008 0.13721 0.12006 0.10672 0.09605 0.08732 0.08004 0.07388 0.06861 0.06403 0.06003
0.04002 0.03694 0.03430 0.03202 0.03002 0.02825 0.02668 0.02528 0.02401 0.02287 0.02183 0.02088 0.02001 0.01921 0.01847 0.01715 0.01601 0.01501 0.01412 0.01334 0.01201
4
4 1 ∕ 2
5
5 1 ∕ 2
6 7 8 9
10 11 12 13 14 15 16
Constants Used for Measuring Pitch Diameters of Metric Screws by the Three-wire System
Pitch in mm
0.866025 P in Inches
Pitch in mm
0.866025 P in Inches
Pitch in mm
0.866025 P in Inches
W in Inches
W in Inches
W in Inches
0.2
0.00682
0.00455 0.00568 0.00682 0.00796 0.00909 0.01023 0.01137 0.01364
0.75 0.02557
0.01705 0.01818 0.02273 0.02841 0.03410 0.03978 0.04546 0.05683
3.5
0.11933
0.07956
0.25 0.00852
0.8
0.02728 0.03410
4
0.13638 0.09092 0.15343 0.10229 0.18753 0.12502 0.20457 0.13638 0.30686 0.18184 0.17048 0.11365
0.3
0.01023
1
4.5
0.35 0.01193
1.25 0.04262
5
0.4
0.01364
1.5
0.05114
5.5
0.45 0.01534
1.75 0.05967
6 8
0.5 0.6 0.7
0.01705 0.02046 0.02387
2
0.06819 0.08524 0.10229
2.5
… … …
0.01591 … … … This table may be used for American National Standard Metric Threads. The formulas for American Standard Unified Threads on page 2128 are used. In the table above, the values of 0.866025 P and W are in inches so that the values for E and M calculated from the formulas on page 2128 are also in inches. 3 0.06819
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