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