Related Resources: gears

### Metric and American Gear Equivalents Table 2

Gears Engineering and Design

Metric and American Gear Equivalents Table 2 for sizes 7.2571 to 203.2".

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 7.2571 3.5 0.4329 10.996 0.2164 5.4979 0.1378 3.500 7.8154 3.25 0.4020 10.211 0.2010 5.1054 0.1279 3.250 8 3.1750 0.3927 9.974 0.1964 4.9886 0.1250 3.175 8.4667 3 0.3711 9.426 0.1855 4.7130 0.1181 3.000 9 2.8222 0.3491 8.867 0.1745 4.4323 0.1111 2.822 9.2364 2.75 0.3401 8.639 0.1700 4.3193 0.1082 2.750 10 2.5400 0.3142 7.981 0.1571 3.9903 0.1000 2.540 10.1600 2.50 0.3092 7.854 0.1546 3.9268 0.0984 2.500 11 2.3091 0.2856 7.254 0.1428 3.6271 0.0909 2.309 11.2889 2.25 0.2783 7.069 0.1391 3.5344 0.0886 2.250 12 2.1167 0.2618 6.646 0.1309 3.3325 0.0833 2.117 12.7000 2 0.2474 6.284 0.1236 3.1420 0.0787 2.000 13 1.9538 0.2417 6.139 0.1208 3.0696 0.0769 1.954 14 1.8143 0.2244 5.700 0.1122 2.8500 0.0714 1.814 14.5143 1.75 0.2164 5.497 0.1082 2.7489 0.0689 1.750 15 1.6933 0.2094 5.319 0.1047 2.6599 0.0667 1.693 16 1.5875 0.1964 4.986 0.0982 2.4936 0.0625 1.587 16.9333 1.5 0.1855 4.712 0.0927 2.3562 0.0591 1.500 18 1.4111 0.1745 4.432 0.0873 2.2166 0.0556 1.411 20 1.2700 0.1571 3.990 0.0785 1.9949 0.0500 1.270 20.3200 1.25 0.1546 3.927 0.0773 1.9635 0.0492 1.250 22 1.1545 0.1428 3.627 0.0714 1.8136 0.0455 1.155 24 1.0583 0.1309 3.325 0.0655 1.6624 0.0417 1.058 25.4000 1 0.1237 3.142 0.0618 1.5708 0.0394 1.000 28 0.90701 0.1122 2.850 0.0561 1.4249 0.0357 0.9071 28.2222 0.9 0.1113 2.827 0.0556 1.4137 0.0354 0.9000 30 0.84667 0.1047 2.659 0.0524 1.3329 0.0333 0.8467 31.7500 0.8 0.0989 2.513 0.04945 1.2566 0.0315 0.8000 32 0.79375 0.0982 2.494 0.04909 1.2468 0.0313 0.7937 33.8667 0.75 0.0928 2.357 0.04638 1.1781 0.0295 0.7500 36 0.70556 0.0873 2.217 0.04363 1.1083 0.0278 0.7056 36.2857 0.7 0.0865 2.199 0.04325 1.0996 0.0276 0.7000 40 0.63500 0.0785 1.994 0.03927 0.9975 0.0250 0.6350 42.3333 0.6 0.0742 1.885 0.03710 0.9423 0.0236 0.6000 44 0.57727 0.0714 1.814 0.03570 0.9068 0.0227 0.5773 48 0.52917 0.0655 1.661 0.03272 0.8311 0.0208 0.5292 50 0.50800 0.0628 1.595 0.03141 0.7976 0.0200 0.5080 50.8000 0.5 0.06184 1.5707 0.03092 0.7854 0.0197 0.5000 63.5000 0.4 0.04947 1.2565 0.02473 0.6283 0.0157 0.4000 64 0.39688 0.04909 1.2469 0.02454 0.6234 0.0156 0.3969 67,7333 0.375 0.04638 1.1781 0.02319 0.5890 0.0148 0.3750 72 0.35278 0.04363 1.1082 0.02182 0.5541 0.0139 0.3528 72.5714 0.35 0.04329 1.0996 0.02164 0.5498 0.0138 0.3500 78.1538 0.325 0.04020 1.0211 0.02010 0.5105 0.0128 0.3250 80 0.31750 0.03927 0.9975 0.01964 0.4987 0.0125 0.3175 84.6667 0.3 0.03711 0.9426 0.01856 0.4713 0.0118 0.3000 92.3636 0.275 0.03401 0.8639 0.01700 0.4319 0.0108 0.2750 96 0.26458 0.03272 0.8311 0.01636 0.4156 0.0104 0.2646 101.6000 0.25 0.03092 0.7854 0.01546 0.3927 0.00984 0.2500 120 0.21167 0.02618 0.6650 0.01309 0.3325 0.00833 0.2117 125 0.20320 0.02513 0.6383 0.01256 0.3192 0.00800 0.2032 127.0000 0.2 0.02474 0.6284 0.01237 0.3142 0.00787 0.2000 150 0.16933 0.02094 0.5319 0.01047 0.2659 0.00667 0.1693 169.3333 0.15 0.01855 0.4712 0.00928 0.2356 0.00591 0.1500 180 0.14111 0.01745 0.4432 0.00873 0.2216 0.00555 0.1411 200 0.12700 0.01571 0.3990 0.00786 0.1995 0.00500 0.1270 203.2000 0.125 0.01546 0.3927 0.00773 0.1963 0.00492 0.1250

Tooth form: Straight-sided and full-depth, forming the basis of a family of full-depth interchangeable gears.
Pressure angle: 20°, conforming to worldwide acceptance.
Addendum: Equal to module m, which corresponds to the American practice of 1/Pd 5 addendum.
Dedendum: Equal to 12.5m, which corresponds to the American practice of 1.25/Pd 5 dedendum.
Root radius: Slightly greater than American standards specifications.
Tip radius: A maximum is specified, whereas American standards do not specify. In practice, U.S. manufacturers can specify a tip radius as near zero as possible.