Related Resources: gears

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