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Metric and American Gear Equivalents Table

Gears Engineering and Design

Metric and American Gear Equivalents Table

The preferred standard gears of the metric system are not interchangeable with the preferred diametral-pitch sizes. The Table below lists commonly used pitches and modules of both systems.

Note that the basic racks for metric and American inch gears are essentially identical, but metric and American standard gears are not interchangeable.

Metric gearing not only is based upon different units of length measure but also involves its own unique design standard. This means that metric gears and American-standard-inch diametral-pitch gears are not interchangeable.

In the metric system the module m is analogous to pitch and is defined as:

m = D / N = mm of pitch diameter per tooth

ISO Metric Gearing Standards

ISO 53 Cylindrical gears for general and heavy engineering Basic rack
ISO 54 Cylindrical gears for general and heavy engineering Modules and diametral pitches
ISO 677 Straight bevel gears for general and heavy engineering Basic rack
ISO 678 Straight bevel gears for general and heavy engineering Modules and diametral pitches
ISO 701 International gear notation—symbols for geometric data
ISO 1122-1 Glossary of gear terms—Part 1: Geometric definitions
ISO 1328 Parallel involute gears—ISO system of accuracy
ISO 1340 Cylindrical gears—Information to be given to the manufacturer by the purchaser in order to obtain the gear required
ISO 1341 Straight bevel gears—Information to be given to the manufacturer by the purchaser in order to obtain the gear required
ISO 2203 Technical drawings—Conventional representation of gears

Tooth proportions for standard spur and helical gears are given in terms of the basic rack. Dimensions, in millimeters, are normalized for module m 5 1. Corresponding values for other modules are obtained by multiplying each dimension by the value of the specific module m. Major tooth parameters are described by this standard:

Metric and American Gear Equivalents Table

Diametral
pitch
Pd
Module
m
Circular
pitch
Circular
tooth
thickness
Addendum
in
mm
in
mm
in
mm
1/2
50.8000
6.2832
159.593
3.1416
79.7965
2.0000
50.8000
0.5080
50
6.1842
157.080
3.0921
78.5398
1.9685
50
0.5644
45
5.5658
141.372
2.7850
70.6858
1.7730
45
0.6048
42
5.1948
131.947
2.5964
65.9734
1.6529
42
0.6513
39
4.8237
122.522
2.4129
61.2610
1.5361
39
0.7056
36
4.4527
113.097
2.2249
56.5487
1.4164
36
3/4
33.8667
4.1888
106.396
2.0943
53.1977
1.3333
33.8667
0.7697
33
4.0816
103.673
2.0400
51.8363
1.2987
33
0.8467
30
3.7105
94.248
1.8545
47.1239
1.1806
30
0.9407
27
3.3395
84.823
1.6693
42.4115
1.0627
27
1
25.4000
3.1416
79.800
1.5708
39.8984
1.0000
25.4001
1.0583
24
2.9685
75.398
1.4847
37.6991
0.9452
24
1.1546
22
2.7210
69.115
1.3600
34.5575
0.8658
22
1.2700
20
2.4737
62.832
1.2368
31.4159
0.7874
20
1.4111
18
2.2263
56.548
1.1132
28.2743
0.7087
18
1.5
16.9333
2.0944
53.198
1.0472
26.5988
0.6667
16.933
1.5875
16
1.9790
50.267
0.9894
25.1327
0.6299
16
1.8143
14
1.7316
43.983
0.8658
21.9911
0.5512
14
2
12.7000
1.5708
39.898
0.7854
19.949
0.5000
12.7000
2.1167
12
1.4842
37.699
0.7420
18.8496
0.4724
12
2.5
10.1600
1.2566
31.918
0.6283
15.9593
0.4000
10.1600
2.5400
10
1.2368
31.415
0.6184
15.7080
0.3937
10
2.8222
9
1.1132
28.275
0.5565
14.1372
0.3543
9
3
8.4667
1.0472
26.599
0.5235
13.2995
0.3333
8.4667
3.1416
8.0851
1.0000
25.400
0.5000
12.7000
0.3183
0.0851
3.1750
8
0.9895
25.133
0.4948
12.5664
0.3150
8.00
3.5
7.2571
0.8976
22.799
0.4488
11.3994
0.2857
7.2571
3.6286
7
0.8658
21.991
0.4329
10.9956
0.2756
7.000
3.9078
6.5
0.8039
20.420
0.4020
10.2101
0.2559
6.5
4
6.3500
0.7854
19.949
0.3927
9.9746
0.2500
6.3500
4.2333
6
0.7421
18.850
0.3710
9.4248
0.2362
6.0000
4.6182
5.5
0.6803
17.279
0.3401
8.6394
0.2165
5.5
5
5.0801
0.6283
15.959
0.3142
7.9794
0.2000
5.080
5.0802
5
0.6184
15.707
0.3092
7.8537
0.1968
5.000
5.3474
4.75
0.5875
14.923
0.2938
7.4612
0.1870
4.750
5.6444
4.5
0.5566
14.138
0.2783
7.0688
0.1772
4.500
6
4.2333
0.5236
13.299
0.2618
6.6497
0.1667
4.233
6.3500
4
0.4947
12.565
0.2473
6.2827
0.1575
4.000
6.7733
3.75
0.4638
11.781
0.2319
5.8903
0.1476
3.750
7
3.6286
0.4488
11.399
0.2244
5.6998
0.1429
3.629
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